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interceptor: add zipkin /v2 interceptor (#111)
* interceptor: add zipkin interceptor * Zipkin interceptor multiplexing + running on 9411 * Can receive spans from diverse sources and successfully intercept traces from various serviceNames and IPv* combinations. Verified by examining the data on the Zipkin UI itself by resending to a server running on a different port. * End-to-end serialization tests where we intercept JSON from a wild Zipkin reporter, transform it into trace-proto then to OpenCensus-Go SpanData and then export it with the OpenCensus-Go Zipkin exporter, inspect the JSON and compare it with the final/expected JSON data. Fixes #24 * interceptor/zipkin: add remoteEndpoint to Node.Attributes Zipkin's RemoteEndpoint field is necessary when later on building the dependency graph for Zipkin services. This change ensures that that field is added as an attribute to the Node with keys whose prefix is: "zipkin.remoteEndpoint." e.g. - "zipkin.remoteEndpoint.ipv4" - "zipkin.remoteEndpoint.serviceName" - "zipkin.remoteEndpoint.port" * Fail if Zipkin interceptor and exporter run on same address Fail spectacularly if the Zipkin interceptor and the Zipkin exporter will all be run on the same address. This is because this is a self DOS vector as intercepted spans will be processed by the interceptor, then exported out by the exporter but instead those exported spans will then be sent back to the interceptor and this goes on indefinitely and will just consume memory and resources. To perform this check: a) Compare HostPorts of interceptor vs exporter b) If say "127.0.0.1", "localhost", "" for host and the ports match c) Resolve the IPs for the hosts if any of those steps match return a logical conflict error which will be thrown later. The crash will look something like this ```shell 2018/10/23 18:54:41 Configuration logical error: ZipkinInterceptor address ("127.0.0.1:9411") aka (127.0.0.1 on port 9411) is the same as the interceptor address ("localhost:9411") aka (127.0.0.1 on port 9411) ``` We can now detect any of these clashing configurations: ```yaml interceptors: zipkin: address: "127.0.0.1:9411" exporters: zipkin: endpoint: "http://localhost:9411/api/v2/spans" ``` ```yaml interceptors: zipkin: address: ":9411" exporters: zipkin: endpoint: "http://localhost:9411/api/v2/spans" ``` ```yaml interceptors: zipkin: address: "localhost:9411" exporters: zipkin: endpoint: "http://localhost:9411/api/v2/spans" ``` ```yaml interceptors: zipkin: address: "localhost:9411" exporters: zipkin: endpoint: "http://:9411/api/v2/spans" ``` ```yaml interceptors: zipkin: address: "localhost:9411" exporters: zipkin: endpoint: "http://127.0.0.1:9411/api/v2/spans" ``` and in a case where IP resolution helped, "10.0.0.147" is my local address and I sneakishly tried to get the interceptor on "localhost" which clashes with my local address as per: ```yaml interceptors: zipkin: address: "localhost:9411" exporters: zipkin: endpoint: "http://10.0.0.147:9411/api/v2/spans" ``` we caught it ```shell 2018/10/23 19:01:01 Configuration logical error: ZipkinInterceptor address ("10.0.0.147:9411") aka (10.0.0.147 on port 9411) is the same as the interceptor address ("localhost:9411") aka (10.0.0.147 on port 9411) ``` * Go fmt with Go1.10 to match TravisCI Go1.11's gofmt seems to be more conservating with aligning literal assignments while Go1.10 seems more extravagant. This subtle difference was causing TravisCI failures since TravisCI uses Go1.10. * interceptor/zipkin: handle compressed HTTP bodies Some clients such as Zipkin-Java send HTTP bodies with JSON that's been compressed as "gzip". This change handles "Content-Encoding" values of: * "gzip" * "deflate", "zlib" and decompresses them accordingly * interceptor/zipkin: tests use anagram signature A test that checked for raffled output before used an "xorChecksum" but that's not really always unique. The better way is to use an anagram counter, then create a signature from the serialized map of counted runes. * interceptor/zipkin: address review feedback * Package rename to "zipkinterceptor" --> "zipkininterceptor" * Fix error names * Address feedback from review * move "zipkinRoute" const to the top to make it easily discoverable and not be buried deep in code * set status of zipkin interceptor if we encounter an error while parsing spans. We set the span status to: StatusInvalidArgument and the error message * *zipkin: address feedback from review * Add a comment ot exporter/exporterparse.zipkinExporter that the mutex "mu" protects all the constituent fields * Fix and ensure that node uniqueness is clear, with the proper check from a map lookup but also rename the variable to store nodes to "uniqueNodes" to make for better code readability * README.md + default config.yaml: update interceptors docs and information Added a section in the README.md on the various interceptors and how to change the Zipkin interceptor address * sync.Mutex instead of sync.RWMutex for zipkinExporter.mu
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