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feat(grpc): configurable default headers on shared gRPC client #1656

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36 changes: 30 additions & 6 deletions grpc/client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -41,15 +41,34 @@ const (
ClientTypeMetadataValue = "aggkit"
)

// VersionHeaderInterceptor adds the client version and type headers to all outgoing requests
func VersionHeaderInterceptor() grpc.UnaryClientInterceptor {
// mergeHeaders overlays the configured headers on top of the built-in defaults.
// Configured values win, so x-client-version / x-client-type can be overridden.
// Keys are normalized to lowercase to match gRPC metadata semantics, so a
// mixed-case override (e.g. "X-Client-Type") replaces the default instead of
// adding a duplicate entry.
func mergeHeaders(extra map[string]string) map[string]string {
merged := map[string]string{
ClientVersionMetadataKey: aggkit.Version,
ClientTypeMetadataKey: ClientTypeMetadataValue,
}
for k, v := range extra {
merged[strings.ToLower(k)] = v
}
return merged
}

// HeaderInterceptor returns a unary client interceptor that appends the given
// metadata headers to every outgoing request. Callers build the header set with
// mergeHeaders, which combines the built-in client version/type defaults with
// any per-client overrides.
func HeaderInterceptor(headers map[string]string) grpc.UnaryClientInterceptor {
return func(
ctx context.Context,
method string, req, reply interface{},
cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
// Add version and type headers to context
ctx = metadata.AppendToOutgoingContext(ctx, ClientVersionMetadataKey, aggkit.Version)
ctx = metadata.AppendToOutgoingContext(ctx, ClientTypeMetadataKey, ClientTypeMetadataValue)
for k, v := range headers {
ctx = metadata.AppendToOutgoingContext(ctx, k, v)
}
return invoker(ctx, method, req, reply, cc, opts...)
}
}
Expand All @@ -71,6 +90,11 @@ type ClientConfig struct {

// Retry represents the retry configuration
Retry *RetryConfig `mapstructure:"Retry"`

// Headers are static metadata headers appended to every outgoing request on
// this client. Configured per-client; empty means none. Configured keys
// x-client-version / x-client-type override the built-in defaults.
Headers map[string]string `mapstructure:"Headers"`
}

// WithURL returns a copy of the current ClientConfig with the URL field set to the given value.
Expand Down Expand Up @@ -265,7 +289,7 @@ func NewClient(cfg *ClientConfig) (*Client, error) {
opts := []grpc.DialOption{
grpc.WithTransportCredentials(insecure.NewCredentials()),
grpc.WithConnectParams(connectParams),
grpc.WithUnaryInterceptor(VersionHeaderInterceptor()),
grpc.WithUnaryInterceptor(HeaderInterceptor(mergeHeaders(cfg.Headers))),
}

serviceCfgJSON, err := createServiceConfig(retryCfg)
Expand Down
110 changes: 104 additions & 6 deletions grpc/client_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -527,7 +527,7 @@ func TestValidateRequestTimeout(t *testing.T) {
}
}

func TestVersionHeaderInterceptor(t *testing.T) {
func TestHeaderInterceptor(t *testing.T) {
testMethod := "/test.Service/TestMethod"

t.Run("AddsVersionAndClientTypeHeadersToContext", func(t *testing.T) {
Expand All @@ -539,7 +539,7 @@ func TestVersionHeaderInterceptor(t *testing.T) {
}

// Create the interceptor
interceptor := VersionHeaderInterceptor()
interceptor := HeaderInterceptor(mergeHeaders(nil))

// Create a test context
ctx := context.Background()
Expand Down Expand Up @@ -579,7 +579,7 @@ func TestVersionHeaderInterceptor(t *testing.T) {
}

// Create the interceptor
interceptor := VersionHeaderInterceptor()
interceptor := HeaderInterceptor(mergeHeaders(nil))

// Create a test context with existing metadata
existingMD := metadata.New(map[string]string{
Expand Down Expand Up @@ -631,7 +631,7 @@ func TestVersionHeaderInterceptor(t *testing.T) {
}

// Create the interceptor
interceptor := VersionHeaderInterceptor()
interceptor := HeaderInterceptor(mergeHeaders(nil))

// Create a test context
ctx := context.Background()
Expand All @@ -655,7 +655,7 @@ func TestVersionHeaderInterceptor(t *testing.T) {
}

// Create the interceptor
interceptor := VersionHeaderInterceptor()
interceptor := HeaderInterceptor(mergeHeaders(nil))

// Create a test context
ctx := context.Background()
Expand Down Expand Up @@ -692,7 +692,7 @@ func TestVersionHeaderInterceptor(t *testing.T) {
}

// Create the interceptor
interceptor := VersionHeaderInterceptor()
interceptor := HeaderInterceptor(mergeHeaders(nil))

// Create a test context
ctx := context.Background()
Expand Down Expand Up @@ -721,4 +721,102 @@ func TestVersionHeaderInterceptor(t *testing.T) {
require.Len(t, clientTypeValues, 1, "Should have exactly one client type header")
require.Equal(t, ClientTypeMetadataValue, clientTypeValues[0], "Client type should match ClientTypeMetadataValue")
})

t.Run("AppliesOverriddenHeaderExactlyOnce", func(t *testing.T) {
var capturedCtx context.Context
mockInvoker := func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, opts ...grpc.CallOption) error {
capturedCtx = ctx
return nil
}

interceptor := HeaderInterceptor(mergeHeaders(map[string]string{ClientTypeMetadataKey: "aggkit-aggsender"}))

var req, reply interface{}
var cc *grpc.ClientConn
err := interceptor(context.Background(), testMethod, req, reply, cc, mockInvoker)
require.NoError(t, err)

md, ok := metadata.FromOutgoingContext(capturedCtx)
require.True(t, ok, "Context should contain outgoing metadata")

clientTypeValues := md.Get(ClientTypeMetadataKey)
require.Len(t, clientTypeValues, 1, "Overridden header must appear exactly once, not duplicated")
require.Equal(t, "aggkit-aggsender", clientTypeValues[0])

// The non-overridden default must remain intact.
require.Equal(t, []string{aggkit.Version}, md.Get(ClientVersionMetadataKey))
})

t.Run("AppliesArbitraryConfiguredHeader", func(t *testing.T) {
var capturedCtx context.Context
mockInvoker := func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, opts ...grpc.CallOption) error {
capturedCtx = ctx
return nil
}

interceptor := HeaderInterceptor(mergeHeaders(map[string]string{"x-trace-source": "obs"}))

var req, reply interface{}
var cc *grpc.ClientConn
err := interceptor(context.Background(), testMethod, req, reply, cc, mockInvoker)
require.NoError(t, err)

md, ok := metadata.FromOutgoingContext(capturedCtx)
require.True(t, ok, "Context should contain outgoing metadata")

traceValues := md.Get("x-trace-source")
require.Len(t, traceValues, 1, "Should have exactly one custom header")
require.Equal(t, "obs", traceValues[0])

// Defaults still present alongside the custom header.
require.Equal(t, []string{aggkit.Version}, md.Get(ClientVersionMetadataKey))
require.Equal(t, []string{ClientTypeMetadataValue}, md.Get(ClientTypeMetadataKey))
})
}

func TestMergeHeaders(t *testing.T) {
t.Run("NilReturnsDefaults", func(t *testing.T) {
got := mergeHeaders(nil)
require.Len(t, got, 2)
require.Equal(t, aggkit.Version, got[ClientVersionMetadataKey])
require.Equal(t, ClientTypeMetadataValue, got[ClientTypeMetadataKey])
})

t.Run("EmptyReturnsDefaults", func(t *testing.T) {
got := mergeHeaders(map[string]string{})
require.Len(t, got, 2)
require.Equal(t, aggkit.Version, got[ClientVersionMetadataKey])
require.Equal(t, ClientTypeMetadataValue, got[ClientTypeMetadataKey])
})

t.Run("OverridesClientTypeOnly", func(t *testing.T) {
got := mergeHeaders(map[string]string{ClientTypeMetadataKey: "aggkit-aggsender"})
require.Len(t, got, 2)
require.Equal(t, "aggkit-aggsender", got[ClientTypeMetadataKey])
require.Equal(t, aggkit.Version, got[ClientVersionMetadataKey], "version should keep its default")
})

t.Run("OverridesBothDefaults", func(t *testing.T) {
got := mergeHeaders(map[string]string{
ClientTypeMetadataKey: "custom-type",
ClientVersionMetadataKey: "v9.9.9",
})
require.Len(t, got, 2)
require.Equal(t, "custom-type", got[ClientTypeMetadataKey])
require.Equal(t, "v9.9.9", got[ClientVersionMetadataKey])
})

t.Run("AddsArbitraryHeaderAlongsideDefaults", func(t *testing.T) {
got := mergeHeaders(map[string]string{"x-trace-source": "obs"})
require.Len(t, got, 3)
require.Equal(t, "obs", got["x-trace-source"])
require.Equal(t, aggkit.Version, got[ClientVersionMetadataKey])
require.Equal(t, ClientTypeMetadataValue, got[ClientTypeMetadataKey])
})

t.Run("NormalizesKeyCaseForOverride", func(t *testing.T) {
got := mergeHeaders(map[string]string{"X-Client-Type": "cased"})
require.Len(t, got, 2, "mixed-case override must not create a duplicate entry")
require.Equal(t, "cased", got[ClientTypeMetadataKey])
})
}
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