Method and apparatus for testing request-response service using live connection traffic

[0001] This application is based on Provisional Application Ser. No. 60/189,734, filed Mar. 16, 2000.

[0002] This application includes subject matter that is protected by Copyright Law. All rights reserved.

[0003] 1. Technical Field

[0004] The present invention relates generally to testing a request-response service using live connection traffic. One such request-response service involves high-performance, fault-tolerant HTTP, streaming media and applications delivery over a content delivery network (CDN).

[0005] 2. Description of the Related Art

[0006] It is well-known to deliver HTTP and streaming media using a content delivery network (CDN). A CDN is a self-organizing network of geographically distributed content delivery nodes that are arranged for efficient delivery of digital content (e.g., Web content, streaming media and applications) on behalf of third party content providers. A request from a requesting end user for given content is directed to a “best” replica, where “best” usually means that the item is served to the client quickly compared to the time it would take to fetch it from the content provider origin server. An entity that provides a CDN is sometimes referred to as a content delivery network service provider or CDNSP.

[0007] Typically, a CDN is implemented as a combination of a content delivery infrastructure, a request-routing mechanism, and a distribution infrastructure. The content delivery infrastructure usually comprises a set of “surrogate” origin servers that are located at strategic locations (e.g., Internet network access points, Internet Points of Presence, and the like) for delivering copies of content to requesting end users. The request-routing mechanism allocates servers in the content delivery infrastructure to requesting clients in a way that, for web content delivery, minimizes a given client's response time and, for streaming media delivery, provides for the highest quality. The distribution infrastructure consists of on-demand or push-based mechanisms that move content from the origin server to the surrogates. An effective CDN serves frequently-accessed content from a surrogate that is optimal for a given requesting client. In a typical CDN, a single service provider operates the request-routers, the surrogates, and the content distributors. In addition, that service provider establishes business relationships with content publishers and acts on behalf of their origin server sites to provide a distributed delivery system. A well-known commercial CDN service that provides web content and media streaming is provided by Akamai Technologies, Inc. of Cambridge, Mass.

[0008] CDNSPs may use content modification to tag content provider content for delivery. Content modification enables a content provider to take direct control over request-routing without the need for specific switching devices or directory services between the requesting clients and the origin server. Typically, content objects are made up of a basic structure that includes references to additional, embedded content objects. Most web pages, for example, consist of an HTML document that contains plain text together with some embedded objects, such as .gif or .jpg images. The embedded objects are referenced using embedded HTML directives. A similar scheme is used for some types of streaming content which, for example, may be embedded within an SMIL document. Embedded HTML or SMIL directives tell the client to fetch embedded objects from the origin server. Using a CDN content modification scheme, a content provider can modify references to embedded objects so that the client is told to fetch an embedded object from the best surrogate (instead of from the origin server).

[0009] In operation, when a client makes a request for an object that is being served from the CDN, an optimal or “best” edge-based content server is identified. The client browser then makes a request for the content from that server. When the requested object is not available from the identified server, the object may be retrieved from another CDN content server or, failing that, from the origin server.

[0010] A well-managed content delivery network implements frequent upgrades to its production software, e.g., the software used to provide HTTP content delivery from its edge-based content servers. Thus, for example, as new content or “edge” server functionalities are added to the network, they need to be tested, debugged, rewritten and, ultimately, deployed into production across the network as a whole. An ongoing challenge is testing such new software is the inability to reproduce real-world workload on new versions of the software short of deploying them in the field. While testing a CDN server with real-world traffic (a “live load test”) would be desirable, it has not been possible to do so without having the CDN server interact with the outside world. This interaction may cause significant problems if the version under live test has bugs or otherwise interferes with conventional server functions. Additionally, when field-deployment is used, there is no convenient mechanism for checking if a new version of the software under test produces equivalent output to the old version, namely, the production version.

[0011] Generally, there are a number of known approaches to testing software. Regression testing refers to the technique of constructing test cases and executing the software against those cases. Regression testing, while effective in avoiding repeat of bugs, is labor-intensive and thus costly. Stress or “load” testing refers to the technique of simulating the working environment of the software using a testbed or equivalent architecture. While stress/load testing is useful in evaluating system limits, finding representative workloads to use for the test is always difficult. Trace-based testing refers to the technique of playing back to the software under test a trace of activity obtained from a production version. This technique, although generally useful, may lead to inaccurate conclusions as, in some applications (like a CDN caching server), traces go stale very quickly and/or do not include information that might be needed to evaluate the new version effectively. Field-deployment testing, as its name suggests, refers to the technique of testing a version of the software with a real-world workload. As noted above, when field-deployment is used, there is no convenient way of isolating the software under test from interacting with real users and customers, and there is no mechanism for checking if a new version of the software under test produces equivalent output to the old version, namely, the production version. Error detection is hard, and debugging is difficult because there is limited information capture and the developer is often unable to deploy instrumented code. In addition, during live field-testing, the developer is not able to destructively test the code, i.e., to make the software less robust (e.g., letting it crash) in the face of problems instead of patching over them, in order to assist in tracking down problems.

[0012] It would be desirable to be able to provide a way to test IP-networking-based servers (either software, hardware, or some combination thereof) with live traffic and to compare the results of these tests with currently running CDN traffic. Such a method also could be used to test network-based servers before their actual deployment. The present invention addresses this need in the art.

[0013] The present invention provides for a method and apparatus for comparison of network systems using live traffic in real-time. The inventive technique presents real-world workload in real-time with no external impact (i.e. no impact on customers of the service, nor the system providing the service), and it enables comparison against a production system for correctness verification.

[0014] A preferred embodiment of the invention is a testing tool for the pseudo-live testing of CDN content staging servers, although this is not a limitation of the invention. When deployed, production content staging servers (also referred to as reverse proxies or surrogate origin servers) sit behind a switch providing connectivity to the Internet. These switches often have a port-monitoring feature, used for management and monitoring, which allows all traffic going through the switch to be seen on the configured port. According to the invention, traffic between clients and the live production CDN servers is monitored by a simulator device, which replicates this workload onto a system under test (SUT). The simulator provides high-fidelity duplication (ideally down to the ethernet frame level), while also compensating for differences in the output between the system under test and the live production system. Additionally, the simulator detects divergences between the outputs from the SUT and live production servers, allowing detection of erroneous behavior. To the extent possible, the SUT is completely isolated from the outside world so that errors or crashes by this system do not affect either the CDN customers or the end users. Thus, the SUT does not interact with end users (i.e., their web browsers). Consequently, the simulator serves as a proxy for the clients. By basing its behavior off the packet stream sent between client and the live production system, the simulator can simulate most of the oddities of real-world client behavior, including malformed packets, timeouts, dropped traffic and reset connections, among others.

[0015] In a preferred embodiment, the main functionality of the tool is provided by an External World Simulator (EWS). The EWS listens promiscuously on a CDN region switch interface, rewrites incoming client packets bound for a production server to be routed to a beta server being tested, optionally compares the content and headers of the beta reply to the production reply, and black-holes (i.e. terminates) the client bound traffic from the beta server. A primary advantage this tool provides is the ability to put servers of an unknown quality into a live environment and to receive notification if the client experience differs from a known standard (as provided by the production servers).

[0016] The simulator may provide varying degrees of validation. Thus, for example, the simulator may provide substantially limited validation that suffices for testing new versions for crashes and long-term memory leaks. The simulator may test for “identical” output, wherein the output of the system under test is checked for byte-for-byte equality with the production system. The simulator may also check for “equivalent” output, wherein the output of the SUT and the production system are checked for logical equivalence (isomorphism). This type of validation typically involves use of specific application-level logic. The particular equivalence checking logic will depend on the functionalities being implemented, of course.

[0017] The foregoing has outlined some of the more pertinent features and technical advantages of the present invention. These features and advantages should be construed to be merely illustrative. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention as will be described. Accordingly, other features and a fuller understanding of the invention may be had by referring to the following Detailed Description of the Preferred Embodiment.

[0025] FIG. 1 is a diagram showing an illustrative content delivery network in which the present invention may be implemented. The content delivery service comprises a preferably global content delivery network (CDN) 100 of content delivery server regions 102a–n, a domain name service (DNS) system 104, and a content modification or “initiator” tool 106 that allows content to be tagged for inclusion on the network. DNS system 104 receives network mapping data from a map maker 107, which receives inputs from monitoring agents 109 distributed throughout the Internet. Agents typically perform various tests and monitor traffic conditions to identify Internet congestion problems. The map maker 107 takes the data generated from the agents and generates one or more maps detailing Internet traffic conditions. Generally, the content delivery service allows the network of content delivery server regions 102a–n to serve a large number of clients efficiently. Each region may include one or more content servers, with multiple content servers typically sharing a local area network (LAN) backbone. Although not meant to be limiting, a typical server is an Intel Pentium-based caching appliance running the Linux operating system with a large amount of RAM and disk storage. As also seen in FIG. 1, the content delivery service may include a network operations control center (NOC) 112 for monitoring the network to ensure that key processes are running, systems have not exceeded capacity, and that subsets of content servers (the so-called CDN regions 102) are interacting properly. A content provider operates an origin server (or server farm) 115 from which requesting end users 119 would normally access the content provider's Web site via the Internet. Use of the CDN avoids transit over the Internet for selected content as described below. The content provider may also have access to a monitoring suite 114 that includes tools for both real-time and historic analysis of customer data.

[0026] High-performance content delivery is provided by directing requests for web objects (e.g., graphics, images, streaming media, HTML and the like) to the content delivery service network. In one known technique, known as Akamai FreeFlow content delivery, HTTP and/or streaming media content is first tagged for delivery by the tool 106, which, for example, may be executed by a content provider at the content provider's web site 115. The initiator tool 106 converts URLs that refer to streaming content to modified resource locators, called ARLs for convenience, so that requests for such media are served preferentially from the CDN instead of the origin server. When an Internet user visit's a CDN customer's site (e.g., origin server 115) and, for example, selects a link to view or hear streaming media, the user's system resolves the domain in the ARL to an IP address. In particular, because the content has been tagged for delivery by the CDN, the URL modification, transparent to the user, cues a dynamic Domain Name Service (dDNS) to query a CDN name server (or hierarchy of name servers) 104 to identify the appropriate media server from which to obtain the stream. The CDN typically implements a request-routing mechanism (e.g., under the control of maps generated from the monitoring agents 109 and map maker 107) to identify an optimal server for each user at a given moment in time. Because each user is served from the optimal streaming server, preferably based on real-time Internet conditions, streaming media content is served reliably and with the least possible packet loss and, thus, the best possible quality. Further details of a preferred dDNS-based request-routing mechanism are described in U.S. Pat. No. 6,108,703, which is incorporated herein by reference.

[0027] FIG. 2 is a representative CDN content server 200. Typically, the content server 200 is a Pentium-based caching appliance running an operating system kernel 202 (e.g., based on Linux), a file system cache 204, CDN global host (or “ghost”) software 206, TCP connection manager 208, and disk storage 210. CDN ghost software 206 is useful to create a “hot” object cache 212 for popular objects being served by the CDN. In operation, the content server 200 receives end user requests for content, determines whether the requested object is present in the hot object cache or the disk storage, serves the requested object via HTTP (if it is present) or establishes a connection to another content server or an origin server to attempt to retrieve the requested object upon a cache miss. In a CDN such as described above with respect to FIG. 1, a set of CDN content servers may be organized and managed together in a peer-to-peer manner as a CDN region. FIG. 3 illustrates one such CDN region. In this example, which is merely representative, the CDN region comprises two (2) sets of four (4) production servers 300a–h that are interconnected over a common backnet 302, which may be a conventional ethernet 100BT switch as illustrated. One or more ethernet swithes 304a–b may be used as a front end to interconnect the CDN region to the public Internet 306, an intranet, a virtual private network, or the like. Although not meant to be limiting, the production servers may be architectured as illustrated in FIG. 2 and described above.

[0028] A well-managed CDN has production servers that are frequently upgraded and enhanced with new software version. As a CDN grows in size, however, it becomes very difficult to test such new software and/or software versions given the scale of the network, the size of the codebase, the problems and deficiencies associated with laboratory or field-testing that have been discussed above. The present invention addresses this problem through a novel live-load systems testing infrastructure and methodology which are now illustrated and described.

[0029] FIG. 4 illustrates an implementation of the testing infrastructure 400 in the context of a CDN region, which is an exemplary application testing environment. In this example, the infrastructure comprises an External World Simulator 402 that sits between the production system and the system under test (SUT) 404. The EWS listens promiscuously on a CDN region switch interface, rewrites incoming client packets bound for a production server to be routed to a beta server being tested, optionally compares the content and headers of the beta reply to the production reply, and black-holes (i.e. terminates) the client bound traffic from the beta server. An advantage this tool provides is the ability to put servers of an unknown quality into a live environment and to receive notification if the client experience differs from a known standard (as provided by the production servers). In this example, the production system is illustrated by the CDN production region comprising four (4) production ghost servers 406a–d and the ethernet front-end switch 408. The backnet is omitted for clarity. The SUT comprises a set of four (4) so-called “invisible” ghost servers 410a–d and the front-end switch 412. A backnet may be used as well. Preferably, there is one invisible ghost server under test for every production ghost server, although this is not a requirement. As noted above, the External World Simulator 402 monitors live traffic between the live production system and requesting clients (not shown) and replicates this workload onto the SUT 404. The EWS 402 provides high fidelity duplication (ideally down to the ethernet frame level), while compensating for differences in the output between the SUT and the live production system. Additionally, the EWS detects divergences between the outputs for corresponding pairs of SUT and live production servers (e.g., servers 406a and 410a, 406b and 410b, etc.), thereby allowing detection of erroneous behavior.

[0030] Although FIG. 4 illustrates a SUT with multiple invisible ghosts, this is not a limitation. The number of machines under test is variable, and may include just a single invisible ghost server, a full region of servers (such as illustrated), multiple regions, and the like. In addition, while preferably the infrastructure uses live system load for testing (i.e., CDN traffic is monitored and its traffic replicated in real-time to drive the SUT), a recorded trace may be captured by the EWS and replayed to the SUT at a later time for testing purposes.

[0031] The term “invisible” is merely a shorthand reference to the fact that the SUT is completely isolated from the outside world so that errors or crashes by this system do not affect either the CDN's customers (content providers) or end users. In particular, the basic constraint that is enforced is that the SUT never interacts with end users (namely, their web browsers). Consequently, the EWS serves as a proxy for the clients. By basing its behavior off the packet stream sent between clients and the live production system, the External World Simulator can simulate most of the oddities of real-world client behavior including, without limitation, malformed packets, timeouts, dropped traffic and reset connections. Ideally, the SUT is able to emulate all outside entities (e.g., end user web browsers, customer web servers, DNS servers, network time services, and the like) to which the production ghost server talks in a conventional CDN operation.

[0032] Although not meant to be limiting, the EWS preferably is a dual NIC, Intel/Linux-based machine running appropriate control routines for carrying out the above-described testing functionality. The production environment may be any commercial or proprietary Internet-, intranet- or enterprise-based content delivery network. An advantage this tool provides is the ability to put servers of an unknown quality into a live environment and to receive notification if the client experience differs from a known standard (as provided by the production servers). The tool may be augmented to allow one to route traffic from multiple production servers at a single test server—enabling a more realistic performance projection tool. In addition, to handle greater throughout, HTTP comparison can be disabled.

[0033] EWS enables monitoring of a production system to generate network-packet level accurate traffic. This provides an extremely high-fidelity workload for the test system. The external interaction may be at selectable test levels such as: HTTP request, IP packet, IP packet and timing, IP packet, timing and fragmentation. The EWS preferably handles various protocols, such as HTTP, HTTPS, and the like. The SUT response stream validation can be of varying degrees, such as limited, identical output and/or equivalent output. Thus, for example, the simulator may provide substantially limited validation that suffices for testing new versions for crashes and long-term memory leaks. The simulator may test for “identical” output, wherein the output of the system under test is checked for byte-for-byte equality with the production system. The simulator may also check for “equivalent” output, wherein the output of the SUT and the production system are checked for logical equivalence (isomorphism). This type of validation typically involves use of specific application-level logic (e.g., checking dates in HTTP headers to determine if two different versions of an object being returned to a requesting client are valid comparing the output of persistent multi-GET connection versus several simple GET requests, etc.). The particular equivalence checking logic will depend on the functionalities being implemented, of course. As noted above, the scale of the system under test may be a single server (or given processes or programs running thereon), a full region of servers, multiple regions, and the like, and the testing environment may be used with live system load or with recorded client traces.

[0034] FIG. 5 illustrates one possible implementation of the External World Simulator. The EWS 500 comprises a set of software modules: a collector 502, a state machine 504, a logger 506, an emitter 508, and a comparator 510. Preferably, the modules communicate via frame queues and operate in both time-slice and threaded modes of operations. The collector 502 is responsible for acquiring packets from the network, preferably using a sniffing library routine, and it also receives responses from the invisible ghosts (because it is the entry point for the EWS). In particular, and although not meant to be limiting, preferably the collector 502 takes advantage of the port-monitoring feature of existing ethernet switches in the CDN region. The port-monitoring feature, used for management and monitoring, allows all traffic going through the switch to be seen on the configured port. The collector 502 pulls traffic from the switch port-monitor (using the sniffing library), performs filtering for interesting packets (e.g., HTTP traffic on the production ghost server), and then feeds those packets into the state machine 504 and the logger 506. The state machine 504 is the core logic of the EWS. It decides what packets should be sent and when. The state machine opens and closes connections between the participating entities, namely, the client, the production ghost server, and the invisible ghost server, as will be described in more detail below. The state machine also absorbs invisible ghost server responses to ensure that the SUT never interacts with the production servers. In particular, these response packets follow the path through the collector (the input to the EWS), and the state machine recognizes them as client-bound traffic and absorbs them.

[0035] As illustrated, the state machine 504 feeds packets into the emitter 508 and the comparator 510. The emitter 508 sends packets onto the network if needed, and isolates the state machine from the other functions. The comparator 510 assembles HTTP requests/responses from the TCP packets. It performs equivalence checking (depending on the application logic included) between the production ghost response and that of the invisible ghost. In one example, the checking verifies that HTTP response codes match. There may be some cases when the codes match but the content handed back (from the respective production ghost and the invisible ghost) differs, or the response code may not match when the content handed back is the same, and so on. The comparator may filter the data based on given criteria. Typically, the comparator writes given data to a log for later analysis. The comparator typically is HTTP-specific, and the other modules need not have any knowledge of what protocol is being used.

[0036] As noted above, the various modules that comprise the EWS enable the EWS to masquerade (to the SUT) as clients. As connections are opened and closed, the EWS duplicates the TCP traffic flowing through the production system. It parses the ghost TCP streams into HTTP responses, checks for equivalence (or other application-level logic validation), records mismatches for human or automated analsyis, and facilitates performance analyis of the SUT or the components thereof. As noted above, the EWS (specifically, the state machine) absorbs or “black-holes” the SUT responses passed from the invisible ghosts through the collector to isolate the SUT from the real-world.

[0037] FIGS. 6–7 illustrate state changes of the state machine in response to receiving packets from the various endpoints of the connections. Normal TCP connections only have two (2) endpoints, namely, the client and the production server. In the testing infrastructure, on the contrary, three (3) endpoints exist, namely, the client, the production system server and the invisible ghost server. FIG. 6 is the opening state diagram, and FIG. 7 is the closing state diagram. This separation is for clarity and omits some possible states. For instance, the production system may start closing the connection before the invisible system has finished establishing it. In addition, the effect of reset packets is ignored for convenience as those packets are not considered part of a normal traffic flow. Familliarity with basic TCP operation is presumed. In the opening diagram (FIG. 6), the states are denoted by three (3) binary digits, a “1” in the position indicates that a particular packet has been received, and a “0” represents that it has not been received. For the opening states, the leftmost bit represents the client's first ACK, the middle bit the production server SYNACK, and the rightmost bit the invisible server SYNACK. It is assumed that the client SYN has already been received or the state machine would not be entered. There are more control packets sent as part of connection tear-down, as illustrated in the closing diagram (FIG. 7). The relevant packets examined are the invisible ghost fin (I_—FIN), production server fin (P_—FIN), client fin (C_—FIN), and client finack of the client fin (I_—ACK(C_—F). Some packets that are part of the tear-down process for normal TCP connections are not relevant to the state machine. Different line types denote which packet was received that triggered the state change, and optionally what packet was sent as a result (indicated by an S( ), S(A) being an ACK, and S(F) being a FIN). Dashed lines are used for those state changes that include sending out a packet.

[0038] FIGS. 8–14 illustrate representative data generated by the testing infrastructure for a given connection. FIG. 8 illustrates the client-production server conversation for the connection. FIG. 9 illustrates how the EWS duplicates the connection open and how the invisible ghost under test responds. FIG. 10 illustrates how the EWS duplicates the client's first ack packet and the client request. FIG. 11 illustrates the production and invisible ghost responses. FIG. 12 illustrates the client acknowledgement, the EWS acknowledgement and FIN. FIG. 13 illustrates the connection close, and FIG. 14 illustrates a representative comparator report.

[0039] The present invention provides a number of new features and advantages. First, EWS enables monitoring of a production system to generate network-packet level accurate traffic that is then duplicated onto a SUT. This provides an extremely high-fidelity workload for the test system. Second, the output of the system is compared against the results of a running production system, which provides a very detailed check (if the new system is producing the desired results) without requiring the construction of a large number of test cases. Finally, the system under test is subjected to real world workload, but the system has no interactions with the outside.

[0040] The following illustrates various routines and data structures that may be used to implement the EWS modules described above:

[0041]

Collector:
Structure Detail
frame—header—t - frame—header—t is the header structure that occurs inside all frames, a basic unit
of memory management. A frame is the basic unit of allocation in IG. time—stamp is set by the
collector (or replay logic) when a packet is generated. ref—count is a bitmap, indicating which
subsystems have interest in this frame. When becomes zero, the frame should be freed.
typedef struct —frame—header—t {
	u—int32 frameno;
	struct timeval time—stamp;
	u—int16 refcount;
	u—int16 from—our—hw—addr:1;
	u—int16 to—our—hw—addr:1;
	u—int16 pad:13;
	u—int16 packet—size;
	u—int16 frame—size
	u—int16 ip—start;
	u—int16 tcp—start;
	u—int16 ip—tot—len;
	u—int32 ip—csum;
	u—int32 tcp—csum;
	u—int32 * page—cnt;
	struct —frame—t * sm—qnext;
} frame—header—t;
	Fields:
	frameno	unique id, used for debugging
	time—stamp	time of receipt of packets
	refcount	reference count, used to determine frame liveness
	from—our—hw—addr:1	indicates whether frame originated locally
	to—our—hw—addr:1	indicates whether frame originated elsewhere
	pad:13	bits reserved for future use
	packet—size	size of payload in this frame
	frame—size	size of this frame, not including the header
	ip—start	byte offset of ip data in the data area
	tcp—start	byte offset of tcp header in the data area
	ip—tot—len	length of ip payload, in bytes
	ip—csum	calc'ed during copy from collector
	tcp—csum	calc'ed during copy from collector
	page—cnt	pointer to counter used for batch frame allocation
	sm—qnext	linking pointer used by state machine.
frame—t - frames hold packet data inside IG. The actual length of the data array is stored in
hdr.frame—size; Data contains the IP packet/fragment.
typedef struct —frame—t {
	frame—header—t hdr;
	byte data[4];
} frame—t;
	Fields:
	hdr	frame header
	data[4]	byte array holding packet data.
frame—ptr—array—t - the frame—ptr—array—t is a structure holding a fixed number of pointers to
frame. It is used to pass frames from the collector to the state machine and logger.
typedef struct —frame—ptr—array—t {
	struct —frame—ptr—array—t * next;
	u—int32 n—ptrs;
	frame—t * frm—ptrs[PTRS—PER—FPA];
} frame—ptr—array—t;
	Fields:
	next	used for linked listing
	n—ptrs	number of live pointers in the array
	frm—ptrs[PTRS—PER—FPA]	array of frame pointers
Routine Detail
frm—collector—frame—alloc
Allocated as frame for use by the collector. The frame—size argument specifies the data payload
size of the frame. The frame header is initialized by this routine, but the frame data is not zero
filled.
frame—t * frm—collector—frame—alloc(	u—int16	frame—size,
	frm—blk—t**	fb)
	Parameters:
	frame—size	size of frame to be allocated
	Returns:
	frame—t	* allocated frame, not necessarily zero-filled, NULL if unable to allocate
		frame.
frm—fpa—alloc
allocates frame pointer arrays
frame—ptr—array—t * frm—fpa—alloc( )
	Returns:
	frame—ptr—array	is successful, NULL if unable to allocate
	Notes:
	Uses an internal memory pool, using the first word of each element as a chaining pointer.
	Allocates in groups of fpa—increment.
frm—fpa—free
frees frame pointer array
void frm—fpa—free( frame—ptr—array—t * fpa)
	Parameters:
	fpa	frame pointer array to free
frm—frame—set—interest
Sets reference count bits indicating specified sources using the frame. Any module is allowed to
set bits indicating that another module will be processing this frame. It is not an error to set an
interest bit that is already set.
void frm—frame—set—interest(	frame—t *	frm,
	u—int8	interest—bits)
	Parameters:
	frm	frame of interest
	interest—bits	bit mask sources of interest.
	Example:
	// logger is in replay mode, wants to make frames
	// of interest to state machine before handing off.
	frame—t * frm;
	// . . . read frame from disk
	frm—frame—set—interest(frm, FRM—BIT—SM);
	// queue frame to state machine
frm—frame—clear—interest
Clears the interest bit indicated by the model. An module should only clear its own interest bit. If
them mask drops to zero, the frame will be freed as a side effect of this routine. Clearing an
already clear bit is an error.
void frm—frame—clear—interest(	frame—t *	frm,
	u—int8	interest—bit)
	Parameters:
	frm	frame of interest
	interest—bit	bit to clear
frm—blk—frame—clear—interest
Clears interest bit in all the frames in the frame block
extern void frm—blk—frame—clear—interest(	frm—blk—t *	blk,
	u—int8	interest—bit)
	Parameters:
	blk	Block of interest
	interest—bit	interest bit to be cleared
State Machine:
Routine Detail
sm—init
configuration entry point of state machine
extern void sm—init(config—info—t * ci)
	Parameters:
	ci	configuration information
sm—dowork
event entry point of state machine system. Will yield after procesing yield—frames (or slightly
more) or when runs out of work.
extern void sm—dowork(u—int32 yield—frames)
	Parameters:
	yield—frames	after how many frames to yield.
sm—shutdown
Called on shutdown. Use to dump summary stats, etc
void sm—shutdown( v oid)
Routine Detail
sti—update—cur—time (internal)
update notion of current time.
void sti—update—cur—time( )
sti—delayed—ack—timeout (internal)
update/start delayed partial ack timer
void sti—delayed—ack—timeout(	sm—state—ply—t *	ply,
	u—int32	ackval)
	Parameters:
	ply	connection to update
	ackval	value to ack
sti—drain—ack—timeout (internal)
update/start drain ack timer
void sti—drain—ack—timeout(sm—state—ply—t * ply)
	Parameters:
	ply	connection to update
sti—set—zero—timeout (internal)
set zero timer. basically means there is more ci data to send.
void sti—set—zero—timeout(sm—state—ply—t * ply)
	Parameters:
	ply	connection to update
sti—set—cfn—delay—timeout (internal)
don't delay sending the CFN too long.
void sti—set—cfn—delay—timeout(sm—state—ply—t * ply)
	Parameters:
	ply	connection to update
sti—delayed—ack—timeout—cancel (internal)
Cancel delayed ack timer
void sti—delayed—ack—timeout—cancel(sm—state—ply—t * ply)
	Parameters:
	ply	connection to update
sti—update—idle—timeout (internal)
update idle timer for the connection
void sti—update—idle—timeout(sm—state—t * state)
	Parameters:
	state	connection to update
sti—restart—idle—timeout (internal)
Restart idle timeout, or indicate connection death
u—int32 sti—restart—idle—timeout(sm—state—t * state)
	Parameters:
	state	connection to update
	Returns:
	0	connection should be terminated
	1	connection is ok, idle time reset.
	Notes:
	(internal)
	An idle timeout has expired. Check if state−>last—packet—time to determine if this
	connection has really been idle long enough to be terminated. If connection should be
	kept alive, idle timer is reset.
sti—restart—cfn—timeout (internal)
Restart client fin delay timeout, or indicate fin should be sent.
u—int32 sti—restart—cfn—timeout(sm—state—t * state)
	Parameters:
	state	connection to update
	Returns:
	0	connection should be terminated
	1	connection is ok, idle time reset.
sti—timer—syn—rexmit—start (internal)
Start CSN retransmit timer
void sti—timer—syn—rexmit—start(sm—state—ply—t * ply)
	Parameters:
	ply	state block
sti—timer—syn—rexmit—cancel (internal)
Start CSN retransmit timer
void sti—timer—syn—rexmit—cancel(sm—state—ply—t * ply)
	Parameters:
	ply	state block
sti—set—timeout (internal)
Set or update absolute timer.
void sti—set—timeout(	void **	timer,
	void *	data,
	u—int32	index,
	u—int32	datum,
	struct timeval *	time)
	Parameters:
	timer	pointer to timer to be set or reset
	data	opaque ptr index
	index	integer index
	datum	integer item stored
	time	time to expire
	Notes:
	(internal)
	Upon return *timer will point to the timer. If *timer is non-NULL upon the call, it is a
	presumptive old timer with the same (data,index) and will be freed.
sti—set—rel—timeout (internal)
Update or set relative timer
void sti—set—rel—timeout(	void **	timer,
	void *	data,
	u—int32	index,
	u—int32	datum,
	struct timeval *	rel—time)
	Parameters:
	timer	pointer to timer to be set or reset
	data	opaque ptr index
	index	integer index
	datum	integer item stored
	rel—time	time to expire (from now).
	Notes:
	(internal)
	Same as sti—set—timeout, except computes the absolute time of the timeout based on the
	current time and rel—time.
sti—remove—timeout (internal)
Removes the timeout specified by *timer. Error to remove a non-present timeout. Will set *timer
to NULL on return.
void sti—remove—timeout( void ** timer)
	Parameters:
	timer	pointer to timer
sti—remove—all—timeouts (internal)
Clean up timeouts
void sti—remove—all—timeouts(sm—state—t * state)
	Parameters:
	state	structure to clear
	Notes:
	(internal)
	Removes all timeouts with this state structure, including subtypes.
sti—min—timeout (internal)
determine waiting time
void sti—min—timeout(struct timeval * wait—time)
	Parameters:
	wait—time	see below
	Notes:
	(internal)
	wait—time, on input, should be set to the maximum time (relative to the last call to
	sti—do—expired) that we should block.
	On return wait—time is the time to block for. It will be no more than the input value, and
	possibly shorter.
sti—do—expired (internal)
invoke and remove expired timers
void sti—do—expired( )
	Notes:
	(internal)
	Finds set of expired timers, copies them and calls back smt—expired—timer. It is safe from
	the callback to manipulate the current timer.
Structure Detail
epkt—t - struct containing the head of a TCP packet. Used to building packets from scratch or
rewrite existing packets.
typedef struct—epkt—t {
	struct iphdr ip;
	struct tcphdr tcp;
} epkt—t;
	Fields:
	ip	ip header
	tcp	tcp header
Routine Detail
smu—state—hash (internal)
looks up entry in tcp hash table. Tries both the src and dst pairs as possible keys. src—is—client is
set to TRUE if the src—ip address corresponds to the client, and FALSE otherwise.
sm—state—t * smu—state—hash(	u—int32 src—ip,
	u—int16 src—port,
	u—int32 dst—ip,
	u—int32 dst—port,
	u—int32 src—class,
	u—int32 dst—class,
	u—int16 seq—id)
	Parameters:
	src—ip	ip address of source
	src—port	tcp port of source
	dst—ip	ip address of destination
	dst—port	tcp port of destination
	src—class	SMT—IP—PG, SMT—IP—IG or SMT—IP—CI
	dst—class	SMT—IP—PG, SMT—IP—IG or SMT—IP—CI
	seq—id	DNS sequence id, or 0 for any other protocol.
	Returns:
	−	hash entry, if it exists
	NULL	entry not in table
smu—state—hash—alloc (internal)
Creates a hash entry for the specified datum.
sm—state—t * smu—state—hash—alloc(	u—int32 src—ip,
	u—int16 src—port,
	u—int32 dst—ip,
	u—int32 dst—port,
	u—int32 src—class,
	u—int32 dst—class,
	u—int32 conntype,
	u—int16 seq—id)
	Parameters:
	src—ip	ip address of source
	src—port	tcp port of source
	dst—ip	ip address of destination
	dst—port	tcp port of destination
	src—class	SMT—IP—PG, SMT—IP—IG or SMT—IP—CI
	dst—class	SMT—IP—PG, SMT—IP—IG or SMT—IP—CI
	conntype	on of SM—C—*
	seq—id	DNS sequence id, or 0 for any other protocol.
	Returns:
	−	hash entry, after creating it.
smu—state—hash—free (internal)
Releases memory and pointers to the named hash entry. All removes any times associated with
the state or the type specific state structures.
void smu—state—hash—free(sm—state—t * lamb)
	Parameters:
	lamb	hash entry to be freed.
smu—classify—ip (internal)
Checks an IP address against known tables of invisible and production ghosts, and returns a
classification.
u—int32 smu—classify—ip(u—int32 ip)
	Parameters:
	ip	ip address
	Returns:
	SMT—IP—IG	if address of an invisible ghost
	SMT—IP—PG	if address of a production ghost
	SMT—IP—UN	otherwise.
smu—valid—tcp—packet (internal)
Validates that the packet contains properly checksumed IP header and TCP header and data. As a
side effect, fills in many of the fields.
int smu—valid—tcp—packet(	frame—t *	frm,
	u—int32	ip—start)
	Parameters:
	frm	frame to verify
	ip—start	start of ip data in frame
	Returns:
	0	if not a valid TCP or IP packet
	1	if valid IP packet
	2	if valid TCP packet
	Notes:
	Assumes packet header and payload are aligned on word boundaries.
smu—flush (internal)
Flush any remaining work items before blocking.
void smu—flush( v oid)
smu—forward—frame (internal)
queue frame for emission by the emitter. The sm module is done with the frame. Before the sm
blocks, it should call sm—flush. This frame is known to be a valid IP frame
void smu—forward—frame(frame—t * frm)
	Parameters:
	frm	frame to be forwarded
smu—send—packet (internal)
queue frame for emission by the emitter. This is the fully generic version of the function which
takes all params.
void smu—send—packet(	emt—work—t *	pinfo,
	int	opcode)
	Parameters:
	pinfo	all of the information about the packet-to-be
	opcode	EMT—PK—REWRITE—DATA or EMT—PK—SEND
	Notes:
	send—fin is only examined for opcode type EMT—PK—REWRITE—DATA. Note send—fin
	= 0 means a FIN should be surpressed in the header if it was already there.
smu—cmp—frame (internal)
SM is done with this frame; hand it off to the comparator. Whom is one of
SMT—IP—{IG,PG,UN}. Before the sm blocks, it should call sm—flush.
void smu—cmp—frame(	frame—t *	frm,
	sm—state—t *	state,
	u—int32	whom)
	Parameters:
	frm	frame to comparator
	whom	flag indicating who sent this packet
smu—cmp—done (internal)
Queue end of stream comparision indicator to comp
void smu—cmp—done(sm—state—ply—t * ply)
	Parameters:
	ply	state structure
smu—unknown—connection—frame (internal)
received a frame for whom we can't find a connection;
void smu—unknown—connection—frame(	sm—state—t *	state,
	frame—t *	frm,
	u—int32	whom)
	Parameters:
	state	connection
	frm	frame
	whom	what to with frame
smu—q—drop—all (internal)
Walk a link-list (linked by sm—qnext), freeing (smu—drop—frame'ing) all the frames.
int smu—q—drop—all(	sm—f—t * l)
	Parameters:
	l	sm—f—t list to free
	Returns:
	−	number of packets freed
smu—q—frm (internal)
Insert frame at tail of fifo
void smu—q—frm(	frame—t *	frm,
	sm—f—t *	l)
	Parameters:
	frm	frame to insert
	l	Fifo
smu—enter—timewait (internal)
Entering timewait state; trigger comparision.
void smu—enter—timewait(sm—state—ply—t * ply)
	Parameters:
	ply	state block
smu—send—reset (internal)
generate a reset against the specified packet.
void smu—send—reset(frame—t * frm)
	Parameters:
	frm	packet which triggered the reset
smu—send—ack (internal)
generate an ack packet on the specified connection.
void smu—send—ack(	sm—state—ply—t *	ply
	u—int32	ack,
	u—int32	win)
	Parameters:
	ply	connection state structure
	ack	absolute ack sequence number to send
smu—send—fin (internal)
generate an ack packet on the specified connection.
void smu—send—fin(sm—state—ply—t * ply)
	Parameters:
	ply	connection state structure
smu—send—syn (internal)
generate a SYN packet on the specified connection.
void smu—send—syn(sm—state—ply—t * ply)
	Parameters:
	ply	connection state structure
smu—cmp—state—done (internal)
Queue end of stream comparision indicator to comp
void smu—cmp—state—done(sm—state—t * state)
spc—ack (internal)
Helper function to spc—dack that does ack transmission.
int spc—ack(	sm—state—ply—t *	ply,
	u—int32 *	ack,
	u—int32 *	window)
	Parameters:
	ply	state structure
	ack	ack to send
	window	window to send
	Returns:
	0	if nothing needs to be done
	1	if the ack/window should be sent immediately
	2	if the ack/window sending can be delayed
	Notes:
	(internal)
	Logic: Acks are queued in the order received, and processed in the same order. Loop over
	the queued acks, sending all acks that are less than the last byte of data sent by the
	invisible ghost. If an ack is found to be in the ahead of the data, call smc—determine—ack
	to see if a frame boundary near the ack can be found. If a frame boundary bigger than the
	last sent ack is found, we consider it for sending. This ack is sent if (1) the suggested ack
	equals the recorded ack or (2) force—partial—ack is set. If an ack is fully consumed, we
	delete it.
	Drain states arrive when we expect no more acks from the client, but want to pull all
	remaining data from the invisible ghost. In the drain state, we simply generate an ack
	every time we see there is unacked IG data.
	Once we have started sending acks because of drain, we ignore any clients acks from then
	on.
	Force partial acks is overloaded: in drain mode, force—partial is a signal to generate an
	ack.
spc—data (internal)
Helper function to spc—dack that does data transmission.
void spc—data(	sm—state—ply—t *	ply,
	u—int32 *	data—seq,
	char **	data,
	u—int16 *	data—len,
	frame—t **	frm)
	Parameters:
	ply	state structure
	data—seq	sequence number of data start
	data	pointer to data
	data—len	length of data
	frm	frame which data points into
	Notes:
	(internal)
	Logic: loop over data, sending any data currently allowed by the ig transmission window.
	If the window causes a packet to be fragmented, we fragment it and send it on. Once a
	packet is completely sent, we move it from the outside—window list to the sent—not—acked
	list. Both lists are maintaining in increasing order.
	One complication may arises from HTTP persistent connections. If a browser has a
	persistent connection open to a production ghost (PG), and the PG initiates the close, one
	will typically see the sequence:
	pg—data ci—ack (long pause) pg—fin ci—fin—ack (long pause)
	then when the browser tries to reuse the connection
	c—data p—reset. This is followed by the browser opening a new connection to the server to
	fetch whatever URL-get was reset.
	In order to avoid the IG from processing these URLs twice, we don't send on any client
	data received after a PFN/CFA until we see an IFN. Once the IFN recieved, we push on
	client data, which should then generate a reset.
spc—determine—ack (internal)
determine an ack value
u—int32 spc—determine—ack(	sm—state—ply—t *	ply,
	u—int32	new—ack,
	int	examine—sna)
	Parameters:
	ply	state block
	new—ack	base of new ack
	examine—sna	boolean, wether to look at sent not acked.
	Returns:
	0	if no ack to be generated
	−	0 relative ack otherwise.
	Notes:
	(internal)
	If examine—sna == FALSE, just use ply−>ci.acks + spontaneously acked.
	if there is data in ply−>ig.sent—not—acked, see if it is now covered. Lots of crufty segment
	alignment logic
	Caller should sweep ig.sent not—acked and outside—window.
spc—release—ig—data (internal)
spc—release—ig—data is invokved whenever the EWS sends the IG a new ack. The routine walks
through the invisible ghost sent—not—acked list, looking for packets that have been fully acked.
void spc—release—ig—data(	sm—state—ply—t *	ply,
	u—int32	ack)
	Parameters:
	ply	state block
	ack	new client ack value, 0 relative
spc—release—cli—data (internal)
spc—release—cli—data is invoked whenever the IG sends a greater ack value. The routine walks
through the cli sent—not—acked list, looking for packets that have been fully acked. Uses ply−
>ig.acks as the ack value.
void spc—release—cli—data(sm—state—ply—t * ply)
	Parameters:
	ply	state block
spc—timeout—ack (internal)
The timer associated with a delayed partial ack has gone off. If we have not advanced beyond
that ack, force a partial ack transmission.
void spc—timeout—ack(	sm—state—ply—t *	ply,
	u—int32	ackno)
	Parameters:
	ply	state block
	ackno	delayed ack number
Structure Detail
sm—state—t - primary state vehicle for TCP connections. The index into the hash table will be the
(client ip,prt).
typedef struct—sm—state—t {
	struct—sm—state—t * next;
	struct—sm—state—t * lru—next;
	struct—sm—state—t * lru—prev;
	u—int32 ci—ip;
	u—int32 pg—ip;
	u—int32 ig—ip;
	u—int16 ci—port;
	u—int16 pg—port;
	u—int16 ig—port;
	u—int16 conntype;
	u—int32 hash—index;
	struct timeval last—frame—time;
	void * timer—idle;
	void * type—specific;
	u—int16 ipproto;
	u—int16 rec—pkts;
} sm—state—t;
	Fields:
	next	linked list construction
	lru—next	linked list for old connection removal
	lru—prev	linked list for old connection removal
	ci—ip	client ip address
	pg—ip	production ghost ip address
	ig—ip	invisible ghost address
	ci—port	client TCP port
	pg—port	production ghost TCP port
	ig—port	invisible ghost port
	conntype	which of SM—C—*
	hash—index	index into the hash table for sm
	last—frame—time	timestamp at which last frame arrived
	timer—idle	pointer to idle timer
	type—specific	info specific to conntype
	ipproto	packet protocol (tcp/udp/ip)
	rec—pkts	origin of received packets on this state (ci | ig | pg)
sm—f—t - Helper structure used to maintain FIFO connections. Uses frame−>hdr.sm—qnext for its
linked lists.
typedef struct —sm—f—t {
	frame—t * head;
	frame—t * tail;
} sm—f—t;
	Fields:
	head	head of linked list
	tail	tail of linked list
sm—h—t - Helper structure used inside sm—state—ply—t
typedef struct —sm—h—t {
	u—int32 seqbase;
	u—int32 sent;
	u—int32 acks;
	u—int32 win;
	sm—f—t sent—not—acked;
	sm—f—t outside—window;
	u—int32 fin—sno;
	u—int16 ip—id;
	u—int16 options;
	u—int16 mss;
	u—int16 win—scale;
} sm—h—t;
	Fields:
	seqbase	initial sequence number
	sent	0-relative highest data sequence number sent
	acks	0-relative highest ack sent
	win	current window
	sent—not—acked	link-listed of packets sent, but not acked
	outside—window	data packets outside the send window
	fin—sno	fin sequence number (not zero-relative)
	ip—id	id field of last ip packet seen; used to detect out of order packets
	options	options sent with SYN
	mss	advertised mss
	win—scale	window scale in this direction (currently unused)
	Notes:
	(internal)
	One is maintained for each of the client, production ghost and invisible ghost.
sm—state—ply—t - state holder for play'd (split descriptions)
typedef struct —sm—state—ply—t {
	u—int32 m—state;
	u—int32 syn—retries:27;
	u—int32 cmp—done:1;
	u—int32 reuse—protect:1;
	u—int32 started—draining:1;
	u—int32 timewait:1;
	u—int32 spontaneously—acked;
	u—int32 ci—lastack;
	u—int32 ci—ack;
	u—int32 ci—win;
	void * timer—dack—xmit;
	sm—state—t * sm—state;
	sm—h—t ci;
	sm—h—t pg;
	sm—h—t ig;
	sm—f—t ci—acks;
} sm—state—ply—t;
	Fields:
	m—state	internal TCP state.
	syn—retries:27	syn rexmit counter
	cmp—done:1	flag: has smu—cmp—done been invoked?
	reuse—protect:1	flag: SYN arrived on live connection
	started—draining:1	flag: has a drain mode ack been sent
	timewait:1	flag: wait a bit before removing connection
	spontaneously—acked	number of bytes spontaneously acked
	ci—lastack	last ack sent to ig
	ci—ack	last ack received from ci
	ci—win	last window received from ci
	timer—dack—xmit	timer for DACK rexmit
	sm—state	backpoint to parent
	ci	client state
	pg	production ghost state
	ig	invisible ghost state
	ci—acks	FIFO of client acks ahead of data
	Notes:
	(internal)
	reuse—protect is set when a connection is draining and new a syn from the same client
	(ip/port) arrives. Reuse—protect causes all packets from the pg and client to be thrown
	away, giving the ig a chance to finish the first connection.
	m—state = state bits from internal open state machine or'ed with state bits from close state
	machine << 5;
	The index into the hash table will be the (client ip,prt).
Routine Detail
smt—process—log (internal)
Processes a packet in the tcp subsystem. If processed, the frame may have been freed. Assumes
caller has determined that this a valid TCP/IP frame.
void smt—process—log(	frame—t *	frm,
	sm—state—t *	state)
	Parameters:
	frm	frame to be processed
	state	structure associated with the connection
	Returns:
	0	if processed frame
	1	if did not process frame
smt—process—fwd (internal)
Processes a packet in the tcp subsystem. If processed, the frame may have been freed. Assumes
caller has determined that this a valid TCP/IP frame.
void smt—process—fwd(	frame—t *	frm,
	sm—state—t *	state)
	Parameters:
	frm	frame to be processed
	state	structure associated with the connection
	Returns:
	0	if processed frame
	1	if did not process frame
smt—ply—h—nullx (internal)
Processes a packet in the tcp subsystem. This is the workhorse routine for the state machine.
Preferably, it is split up into 3 sections, depending on where the packet originated from. The
entire state machine can be implemented in one function by noting that the states are path
invariant, i.e., it does not matter how the state was arrived at, only that it is in a given state.
Because of this, behavior can be determined based on specific packets by doing simple checks to
make sure appropriate packets have been seen earlier. In addition to managing the state
according to the state machine, all the data flow/aknowledgement logic is handled either in this
routine or by helper functions. Often, the acks generated by the client will not line up with the
data packets sent by the invisible ghost.
void smt—ply—h—nullx(	sm—state—t *	state,
	frame—t *	frm)
	Parameters:
	state	structure associated with the connection
	frm	frame to be processed
	Returns:
	0	if processed frame
	1	if did not process frame
smt—process—ply (internal)
Processes a packet in a split stream. Assumes caller has determined that this a valid TCP/IP
frame.
void smt—process—ply(	frame—t *	frm,
	sm—state—t *	state)
	Parameters:
	frm	frame to be processed
	state	structure associated with the connection
	Returns:
	0	if processed frame
	1	if did not process frame
smtcp—doframe (internal)
Determines if a packet is part of an existing connection. If not, do we need to create a connection
for it, and if so, what type of connection? If processed, the frame may have been freed. Assumes
caller has determined that this a valid TCP/IP frame.
u—int32 smtcp—doframe(	frame—t *	frm,
	u—int32	ip—start)
	Parameters:
	frm	frame to be processed
	ip—start	byte offset of the start of the TCP header
	Returns:
	0	if processed frame
	1	if did not process frame
smt—ply—free (internal)
Closing down a smt—ply structure. Let the comparator know its time to compare these streams.
static void smt—ply—free(sm—state—ply—t * ply)
	Parameters:
	ply	state block to be freed
smt—idle—timeout (internal)
handle idle timer expiration
void smt—idle—timeout(sm—state—t * state)
	Parameters:
	state	control block of timeout
	Notes:
	(internal)
	Idle timeout has gone off for this connection. The idle timeout of a connection is updated
	lazily, so this does not mean the connection has been necessarily idle for this long. Call
	sti—idle—restart to restart the timer (if not really expired) or otherwise really expire the
	connection.
Logger/Replay:
Design
The logger module is intended to provide the following pieces of functionality.
First, to log all frames as they are gathered by the collector. (Optionally, one might want the
logger to be selective - for example, to only log the client generated packets.)
Second, to be able to play back a saved packet trace, simulating the collector. Additional desired
functionality would be to compare the world simulator output from a saved run to a new run to
check for regression.
Routine Detail
lgg—init
configuration entry point of logging subsystem
extern void lgg—init(	config—info—t *	ci,
	int	nowrite)
	Parameters:
	ci	configuration information
	nowrite	if set, force the logger to not log
lgg—shutdown
Shut down logger/write last disk block
void lgg—shutdown( v oid)
lgg—dowork
event entry point of logging subsystem.
extern void lgg—dowork( )
lgg—replay
Entry point for log replay
int lgg—replay( int tcpdumpmode)
	Parameters:
	tcpdumpmode	(boolean) if set, just dump instead of replaying
	Returns:
	0	if the replay completed successfully.
	Notes:
	The specified log file will be opened in turn and played back. Play back means to send
	each logged packet back through the logger interface and into the state machine
debug—print—frame
tcpdump style description of the packet in frm.
void debug—print—frame(	frame—t *	frm,
	FILE *	filedes)
	Parameters:
	frm	frame to be printed.
	filedes	stream in which to write the information.
	Notes:
	This routine is primarily for debugging.
Comparator:
CWT—PER—CWA - number of cmp—work—t pointers in a cmp—work—array—t
#define CWT—PER—CWA 10
Structure Detail
cmp—work—t - If frame is non-NULL, then this a frame for the comparator to analyze, and type
indicates the source of the frame: SMT—IP—{PG,IG,UN} for invisible ghost, production ghost
and unknown (presumptive client) respectively. If frame is NULL, this packet indicates a set of
flows that ready to compare. Included is a triple of ci, production, and invisible ghost ip and
ports, respectively. The ports are in host order, while the ip addresses are in network order.
typedef struct {
	frame—t * frame;
	u—int32 conn—id;
	u—int32 ci—ip;
	u—int32 pg—ip;
	u—int32 ig—ip;
	u—int16 ci—port;
	u—int16 pg—port;
	u—int16 ig—port;
} cmp—work—t;
	Fields:
	frame	TCP frame
	conn—id	Connection id
	ci—ip	clientip (network order)
	pg—ip	production ghost ip (network order)
	ig—ip	invisible ghost ip (network order)
	ci—port	client port (host order)
	pg—port	production ghost port (host order)
	ig—port	invisible ghost port (host order)
cmp—work—array—t - Batched vector of work items for the comparator to process.
typedef struct —cmp—work—array—t {
	struct —cmp—work—array—t * next;
	u—int32 n—elt;
	cmp—work—t work—elt[CWT—PER—CWA];
} cmp—work—array—t;
	Fields:
	next	next work array in the list
	n—elt	number of live work items
	work—elt[CWT—PER—CWA]	array of work items
Emitter:
Structure Detail
pseudo—hdr—t - The pseudo header for UDP/TCP checksumming as defined by the TCP/IP spec.
typedef struct —pseudo—hdr—t {
	u—int32 saddr;
	u—int32 daddr;
	u—int8 zero;
	u—int8 proto;
	u—int16 len;
} pseudo—hdr—t;
	Fields:
	saddr	source IP address.
	daddr	dest IP address.
	zero	pad byte.
	proto	protocol number.
	len	UDP/TCP packet length including header.
emt—work—t - Contains a single unit of work for the emitter thread.
typedef struct —emt—work—t {
	char * data;
	char options[40];
	frame—t * frm—ptr;
	int opcode;
	u—int32 saddr;
	u—int32 daddr;
	u—int32 seq;
	u—int32 ack;
	u—int32 frm—win;
	u—int16 sport;
	u—int16 dport;
	u—int16 data—len;
	u—int16 opt—len;
	u—int8 flags;
} emt—work—t;
	Fields:
	data	TCP payload pointer.
	options[40]	TCP options.
	frm—ptr	Frame to build new packet off of.
	opcode	Specifies some work to be done on the frame.
	saddr	Source address.
	daddr	Destination address.
	seq	sequence number.
	ack	ack sequence number.
	frm—win	TCP window value
	sport	Source port.
	dport	Destination port.
	data—len	Length of data.
	opt—len	Length of options.
	flags	TCP flags.
	Notes:
	All values which are also contained in network packets are assumed to be in network
	order.
emt—work—array—t - Convenience type for passing around batches of emt—work—t's.
typedef struct —emt—work—array—t {
	struct —emt—work—array—t * next;
	int n—elt;
	emt—work—t work—elt[CWT—PER—EWA];
} emt—work—array—t;
	Fields:
	next	linked list overhead.
	n—elt	Number of emt—work—t's contained herein.
	work—elt[CWT—PER—EWA]	Array of data to be worked on.
Routine Detail
emt—init
Handles initialization for the emitter module.
void emt—init( config—info—t * ci)
	Parameters:
	ci	information read from the config file.
	Returns:
	−1	on error
	0	otherwise
emt—shutdown
Handles shutdown for the emitter module.
void emt—shutdown( )
emt—dowork
Does work for a little while, then yields.
void emt—dowork( )

[0042] Although the present invention has been described and illustrated in the context of testing a CDN content staging server, this is not a limitation of the present invention. One of ordinary skill in the art will recognize that systems infrastructure underlying the present invention is suitable for testing a variety of network-based systems including web servers, proxy servers, DNS name servers, web server plugins, browsers, and the like. Thus, another illustrative production environment is a web hosting environment with the system under test being any generic web server. Moreover, by adapting the test logic used to determine “equivalent output” between a production system and the SUT, real-world workloads can be used to test and validate new functionalities, regardless of the specific nature of the SUT.

[0043] Having thus described our invention, the following sets forth what we now claim.