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

Author: Emmanuel T Odeke

README.md

@@ -22,6 +22,8 @@
     - [Configuration file](#agent-configuration-file)
         - [Exporters](#agent-config-exporters)
         - [Interceptors](#agent-config-interceptors)
+            - [OpenCensus](#details-interceptors-opencensus)
+            - [Zipkin](#details-interceptors-zipkin)
         - [End-to-end example](#agent-config-end-to-end-example)
     - [Docker image](#agent-docker-image)
 - [OpenCensus Collector](#opencensus-collector)
@@ -271,14 +273,36 @@ exporters:
 ```
 
 #### <a name="agent-config-interceptors"></a>Interceptors
+As previously mentioned, the agent provides a couple of interceptors
+
+#### <a name="details-interceptors-opencensus"> OpenCensus
+
+This interceptor receives spans from OpenCensus instrumented applications and translates them into the internal span types that
+are then sent to the collector/exporters.
+
+Its address can be configured in the YAML configuration file under section "intercpetors", subsection "opencensus" and field "address".
 
-To modify the address that the OpenCensus interceptor runs on, please use the
-YAML field name `opencensus_interceptor` and it takes fields like `address`.
 For example:
+```yaml
+interceptors:
+    opencensus:
+        address: "127.0.0.1:55678"
+```
+
+By default this interceptor is ALWAYS started since it is the point of the "OpenCensus agent"
 
+#### <a name="details-interceptors-zipkin"> Zipkin
+
+This interceptor receives spans from Zipkin "/v2" API HTTP uploads and translates them into the internal span types that are then
+sent to the collector/exporters.
+
+Its address can be configured in the YAML configuration file under section "intercpetors", subsection "zipkin" and field "address".
+
+For example:
 ```yaml
-opencensus_interceptor:
-    address: "localhost:55678"
+interceptors:
+    zipkin:
+        address: "localhost:9411"
 ```
 
 ### <a name="agent-config-end-to-end-example"></a>Running an end-to-end example/demo

cmd/ocagent/config.go

@@ -15,7 +15,12 @@
 package main
 
 import (
+	"fmt"
 	"log"
+	"net"
+	"net/url"
+	"reflect"
+	"strings"
 
 	yaml "gopkg.in/yaml.v2"
 
@@ -52,7 +57,8 @@ type config struct {
 }
 
 type interceptors struct {
-	OpenCensusInterceptor *interceptorConfig `yaml:"opencensus"`
+	OpenCensus *interceptorConfig `yaml:"opencensus"`
+	Zipkin     *interceptorConfig `yaml:"zipkin"`
 }
 
 type interceptorConfig struct {
@@ -70,10 +76,10 @@ func (c *config) ocInterceptorAddress() string {
 		return defaultOCInterceptorAddress
 	}
 	inCfg := c.Interceptors
-	if inCfg.OpenCensusInterceptor == nil || inCfg.OpenCensusInterceptor.Address == "" {
+	if inCfg.OpenCensus == nil || inCfg.OpenCensus.Address == "" {
 		return defaultOCInterceptorAddress
 	}
-	return inCfg.OpenCensusInterceptor.Address
+	return inCfg.OpenCensus.Address
 }
 
 func (c *config) zPagesDisabled() bool {
@@ -94,6 +100,24 @@ func (c *config) zPagesPort() (int, bool) {
 	return port, true
 }
 
+func (c *config) zipkinInterceptorEnabled() bool {
+	if c == nil {
+		return false
+	}
+	return c.Interceptors != nil && c.Interceptors.Zipkin != nil
+}
+
+func (c *config) zipkinInterceptorAddress() string {
+	if c == nil || c.Interceptors == nil {
+		return exporterparser.DefaultZipkinEndpointHostPort
+	}
+	inCfg := c.Interceptors
+	if inCfg.Zipkin == nil || inCfg.Zipkin.Address == "" {
+		return exporterparser.DefaultZipkinEndpointHostPort
+	}
+	return inCfg.Zipkin.Address
+}
+
 func parseOCAgentConfig(yamlBlob []byte) (*config, error) {
 	var cfg config
 	if err := yaml.Unmarshal(yamlBlob, &cfg); err != nil {
@@ -102,7 +126,72 @@ func parseOCAgentConfig(yamlBlob []byte) (*config, error) {
 	return &cfg, nil
 }
 
-type exporterParser func(yamlConfig []byte) (te []exporter.TraceExporter, err error)
+// The goal of this function is to catch logical errors such as
+// if the Zipkin interceptor port conflicts with that of the exporter
+// lest we'll have a self DOS because spans will be exported "out" from
+// the exporter, yet be received from the interceptor, then sent back out
+// and back in a never ending loop.
+func (c *config) checkLogicalConflicts(blob []byte) error {
+	var cfg struct {
+		Exporters *struct {
+			Zipkin *exporterparser.ZipkinConfig `yaml:"zipkin"`
+		} `yaml:"exporters"`
+	}
+	if err := yaml.Unmarshal(blob, &cfg); err != nil {
+		return err
+	}
+
+	if cfg.Exporters == nil || cfg.Exporters.Zipkin == nil {
+		return nil
+	}
+
+	zc := cfg.Exporters.Zipkin
+
+	zExporterAddr := zc.EndpointURL()
+	zExporterURL, err := url.Parse(zExporterAddr)
+	if err != nil {
+		return fmt.Errorf("parsing ZipkinExporter address %q got error: %v", zExporterAddr, err)
+	}
+
+	zInterceptorHostPort := c.zipkinInterceptorAddress()
+
+	zExporterHostPort := zExporterURL.Host
+	if zInterceptorHostPort == zExporterHostPort {
+		return fmt.Errorf("ZipkinExporter address (%q) is the same as the interceptor address (%q)",
+			zExporterHostPort, zInterceptorHostPort)
+	}
+	zExpHost, zExpPort, _ := net.SplitHostPort(zExporterHostPort)
+	zInterceptorHost, zInterceptorPort, _ := net.SplitHostPort(zExporterHostPort)
+	if eqHosts(zExpHost, zInterceptorHost) && zExpPort == zInterceptorPort {
+		return fmt.Errorf("ZipkinExporter address (%q) aka (%s on port %s)\nis the same as the interceptor address (%q) aka (%s on port %s)",
+			zExporterHostPort, zExpHost, zExpPort, zInterceptorHostPort, zInterceptorHost, zInterceptorPort)
+	}
+
+	// Otherwise, now let's resolve the IPs and ensure that they aren't the same
+	zExpIPAddr, _ := net.ResolveIPAddr("ip", zExpHost)
+	zInterceptorIPAddr, _ := net.ResolveIPAddr("ip", zInterceptorHost)
+	if zExpIPAddr != nil && zInterceptorIPAddr != nil && reflect.DeepEqual(zExpIPAddr, zInterceptorIPAddr) {
+		return fmt.Errorf("ZipkinExporter address (%q) aka (%+v)\nis the same as the\ninterceptor address (%q) aka (%+v)",
+			zExporterHostPort, zExpIPAddr, zInterceptorHostPort, zInterceptorIPAddr)
+	}
+	return nil
+}
+
+func eqHosts(host1, host2 string) bool {
+	if host1 == host2 {
+		return true
+	}
+	return eqLocalHost(host1) && eqLocalHost(host2)
+}
+
+func eqLocalHost(host string) bool {
+	switch strings.ToLower(host) {
+	case "", "localhost", "127.0.0.1":
+		return true
+	default:
+		return false
+	}
+}
 
 // exportersFromYAMLConfig parses the config yaml payload and returns the respective exporters
 func exportersFromYAMLConfig(config []byte) (traceExporters []exporter.TraceExporter, doneFns []func() error) {
@@ -128,6 +217,7 @@ func exportersFromYAMLConfig(config []byte) (traceExporters []exporter.TraceExpo
 				nonNilExporters += 1
 			}
 		}
+
 		if nonNilExporters > 0 {
 			pluralization := "exporter"
 			if nonNilExporters > 1 {

cmd/ocagent/config.yaml

@@ -2,6 +2,9 @@ interceptors:
     opencensus:
         address: "127.0.0.1:55678"
 
+    zipkin:
+        address: "localhost:9411"
+
 exporters:
     stackdriver:
         project: "project-id"

cmd/ocagent/main.go

@@ -29,6 +29,7 @@ import (
 	agenttracepb "github.com/census-instrumentation/opencensus-proto/gen-go/agent/trace/v1"
 	"github.com/census-instrumentation/opencensus-service/exporter"
 	"github.com/census-instrumentation/opencensus-service/interceptor/opencensus"
+	"github.com/census-instrumentation/opencensus-service/interceptor/zipkin"
 	"github.com/census-instrumentation/opencensus-service/internal"
 	"github.com/census-instrumentation/opencensus-service/spanreceiver"
 	"go.opencensus.io/plugin/ocgrpc"
@@ -39,6 +40,8 @@ import (
 var configYAMLFile string
 var ocInterceptorPort int
 
+const zipkinRoute = "/api/v2/spans"
+
 func main() {
 	if err := rootCmd.Execute(); err != nil {
 		log.Fatal(err)
@@ -54,6 +57,14 @@ func runOCAgent() {
 	if err != nil {
 		log.Fatalf("Failed to parse own configuration %v error: %v", configYAMLFile, err)
 	}
+
+	// Ensure that we check and catch any logical errors with the
+	// configuration e.g. if an interceptor shares the same address
+	// as an exporter which would cause a self DOS and waste resources.
+	if err := agentConfig.checkLogicalConflicts(yamlBlob); err != nil {
+		log.Fatalf("Configuration logical error: %v", err)
+	}
+
 	ocInterceptorAddr := agentConfig.ocInterceptorAddress()
 
 	traceExporters, closeFns := exportersFromYAMLConfig(yamlBlob)
@@ -64,7 +75,6 @@ func runOCAgent() {
 	if err != nil {
 		log.Fatal(err)
 	}
-
 	closeFns = append(closeFns, ocInterceptorDoneFn)
 
 	// If zPages are enabled, run them
@@ -74,6 +84,16 @@ func runOCAgent() {
 		closeFns = append(closeFns, zCloseFn)
 	}
 
+	// If the Zipkin interceptor is enabled, then run it
+	if agentConfig.zipkinInterceptorEnabled() {
+		zipkinInterceptorAddr := agentConfig.zipkinInterceptorAddress()
+		zipkinInterceptorDoneFn, err := runZipkinInterceptor(zipkinInterceptorAddr, commonSpanReceiver)
+		if err != nil {
+			log.Fatal(err)
+		}
+		closeFns = append(closeFns, zipkinInterceptorDoneFn)
+	}
+
 	// Always cleanup finally
 	defer func() {
 		for _, closeFn := range closeFns {
@@ -141,3 +161,27 @@ func runOCInterceptor(addr string, sr spanreceiver.SpanReceiver) (doneFn func()
 	doneFn = ln.Close
 	return doneFn, nil
 }
+
+func runZipkinInterceptor(addr string, sr spanreceiver.SpanReceiver) (doneFn func() error, err error) {
+	zi, err := zipkininterceptor.New(sr)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to create the Zipkin interceptor: %v", err)
+	}
+
+	ln, err := net.Listen("tcp", addr)
+	if err != nil {
+		return nil, fmt.Errorf("Cannot bind Zipkin interceptor to address %q: %v", addr, err)
+	}
+	mux := http.NewServeMux()
+	mux.Handle(zipkinRoute, zi)
+	go func() {
+		fullAddr := addr + zipkinRoute
+		log.Printf("Running the Zipkin interceptor at %q", fullAddr)
+		if err := http.Serve(ln, mux); err != nil {
+			log.Fatalf("Failed to serve the Zipkin interceptor: %v", err)
+		}
+	}()
+
+	doneFn = ln.Close
+	return doneFn, nil
+}