Make it possible to propagate correlation ID across processessh-extract-context-from-env

Previously, gitlab-shell did not pass a context through the application.
Correlation IDs were generated down the call stack, since we don't pass
the context around from the start execution.

This has several potential downsides:

1. It's easier for programming mistakes to be made in future which lead
to multiple correlation IDs being generated for a single request.
2. Correlation IDs cannot be passed in from upstream requests
3. Other advantages of context passing, such as distributed tracing is
not possible.

This commit changes the behavior:

1. Extract the correlation ID from the environment at the start of
the application.
2. If no correlation ID exists, generate a random one.
3. Pass the correlation ID to the GitLabNet API requests.

This change also enables other clients of GitLabNet (e.g. Gitaly) to
pass along the correlation ID in the internal API requests
(https://gitlab.com/gitlab-org/gitaly/-/issues/2725).

Fixes https://gitlab.com/gitlab-org/gitlab-shell/-/issues/474

1 files changed, 27 insertions, 1 deletions

diff --git a/internal/command/command.go b/internal/command/command.go
index 283b4a1..7e0617e 100644
--- a/internal/command/command.go
+++ b/internal/command/command.go
@@ -1,6 +1,8 @@
 package command
 
 import (
+	"context"
+
 	"gitlab.com/gitlab-org/gitlab-shell/internal/command/authorizedkeys"
 	"gitlab.com/gitlab-org/gitlab-shell/internal/command/authorizedprincipals"
 	"gitlab.com/gitlab-org/gitlab-shell/internal/command/commandargs"
@@ -16,10 +18,13 @@ import (
 	"gitlab.com/gitlab-org/gitlab-shell/internal/command/uploadpack"
 	"gitlab.com/gitlab-org/gitlab-shell/internal/config"
 	"gitlab.com/gitlab-org/gitlab-shell/internal/executable"
+	"gitlab.com/gitlab-org/labkit/correlation"
+	"gitlab.com/gitlab-org/labkit/log"
+	"gitlab.com/gitlab-org/labkit/tracing"
 )
 
 type Command interface {
-	Execute() error
+	Execute(ctx context.Context) error
 }
 
 func New(e *executable.Executable, arguments []string, config *config.Config, readWriter *readwriter.ReadWriter) (Command, error) {
@@ -35,6 +40,27 @@ func New(e *executable.Executable, arguments []string, config *config.Config, re
 	return nil, disallowedcommand.Error
 }
 
+// ContextWithCorrelationID() will always return a background Context
+// with a correlation ID.  It will first attempt to extract the ID from
+// an environment variable. If is not available, a random one will be
+// generated.
+func ContextWithCorrelationID() (context.Context, func()) {
+	ctx, finished := tracing.ExtractFromEnv(context.Background())
+	defer finished()
+
+	correlationID := correlation.ExtractFromContext(ctx)
+	if correlationID == "" {
+		correlationID, err := correlation.RandomID()
+		if err != nil {
+			log.WithError(err).Warn("unable to generate correlation ID")
+		} else {
+			ctx = correlation.ContextWithCorrelation(ctx, correlationID)
+		}
+	}
+
+	return ctx, finished
+}
+
 func buildCommand(e *executable.Executable, args commandargs.CommandArgs, config *config.Config, readWriter *readwriter.ReadWriter) Command {
 	switch e.Name {
 	case executable.GitlabShell: