Configurable buffer size for reading plugin log lines (#265)

- Add `PluginLogBufferSize` option to ClientConfig, defaulting to previous 64KiB size
- Added a new test `TestClient_logStderrParseJSON` to verify the parsing of JSON formatted logs.

client.go

@@ -73,6 +73,9 @@ var (
 	ErrGRPCBrokerMuxNotSupported = errors.New("client requested gRPC broker multiplexing but plugin does not support the feature")
 )
 
+// defaultPluginLogBufferSize is the default size of the buffer used to read from stderr for plugin log lines.
+const defaultPluginLogBufferSize = 64 * 1024
+
 // Client handles the lifecycle of a plugin application. It launches
 // plugins, connects to them, dispenses interface implementations, and handles
 // killing the process.
@@ -220,6 +223,10 @@ type ClientConfig struct {
 	// it will default to hclog's default logger.
 	Logger hclog.Logger
 
+	// PluginLogBufferSize is the buffer size(bytes) to read from stderr for plugin log lines.
+	// If this is 0, then the default of 64KB is used.
+	PluginLogBufferSize int
+
 	// AutoMTLS has the client and server automatically negotiate mTLS for
 	// transport authentication. This ensures that only the original client will
 	// be allowed to connect to the server, and all other connections will be
@@ -416,6 +423,10 @@ func NewClient(config *ClientConfig) (c *Client) {
 		})
 	}
 
+	if config.PluginLogBufferSize == 0 {
+		config.PluginLogBufferSize = defaultPluginLogBufferSize
+	}
+
 	c = &Client{
 		config: config,
 		logger: config.Logger,
@@ -1146,14 +1157,12 @@ func (c *Client) getGRPCMuxer(addr net.Addr) (*grpcmux.GRPCClientMuxer, error) {
 	return c.grpcMuxer, nil
 }
 
-var stdErrBufferSize = 64 * 1024
-
 func (c *Client) logStderr(name string, r io.Reader) {
 	defer c.clientWaitGroup.Done()
 	defer c.stderrWaitGroup.Done()
 	l := c.logger.Named(filepath.Base(name))
 
-	reader := bufio.NewReaderSize(r, stdErrBufferSize)
+	reader := bufio.NewReaderSize(r, c.config.PluginLogBufferSize)
 	// continuation indicates the previous line was a prefix
 	continuation := false
 

client_test.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"context"
 	"crypto/sha256"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -1483,18 +1484,13 @@ func testClient_logger(t *testing.T, proto string) {
 
 // Test that we continue to consume stderr over long lines.
 func TestClient_logStderr(t *testing.T) {
-	orig := stdErrBufferSize
-	stdErrBufferSize = 32
-	defer func() {
-		stdErrBufferSize = orig
-	}()
-
 	stderr := bytes.Buffer{}
 	c := NewClient(&ClientConfig{
 		Stderr: &stderr,
 		Cmd: &exec.Cmd{
 			Path: "test",
 		},
+		PluginLogBufferSize: 32,
 	})
 	c.clientWaitGroup.Add(1)
 
@@ -1515,3 +1511,55 @@ this line is short
 		t.Fatalf("\nexpected output: %q\ngot output:      %q", msg, read)
 	}
 }
+
+func TestClient_logStderrParseJSON(t *testing.T) {
+	logBuf := bytes.Buffer{}
+	c := NewClient(&ClientConfig{
+		Stderr:              bytes.NewBuffer(nil),
+		Cmd:                 &exec.Cmd{Path: "test"},
+		PluginLogBufferSize: 64,
+		Logger: hclog.New(&hclog.LoggerOptions{
+			Name:       "test-logger",
+			Level:      hclog.Trace,
+			Output:     &logBuf,
+			JSONFormat: true,
+		}),
+	})
+	c.clientWaitGroup.Add(1)
+
+	msg := `{"@message": "this is a message", "@level": "info"}
+{"@message": "this is a large message that is more than 64 bytes long", "@level": "info"}`
+	reader := strings.NewReader(msg)
+
+	c.stderrWaitGroup.Add(1)
+	c.logStderr(c.config.Cmd.Path, reader)
+	logs := strings.Split(strings.TrimSpace(logBuf.String()), "\n")
+
+	wants := []struct {
+		wantLevel   string
+		wantMessage string
+	}{
+		{"info", "this is a message"},
+		{"debug", `{"@message": "this is a large message that is more than 64 bytes`},
+		{"debug", ` long", "@level": "info"}`},
+	}
+
+	if len(logs) != len(wants) {
+		t.Fatalf("expected %d logs, got %d", len(wants), len(logs))
+	}
+
+	for i, tt := range wants {
+		l := make(map[string]interface{})
+		if err := json.Unmarshal([]byte(logs[i]), &l); err != nil {
+			t.Fatal(err)
+		}
+
+		if l["@level"] != tt.wantLevel {
+			t.Fatalf("expected level %q, got %q", tt.wantLevel, l["@level"])
+		}
+
+		if l["@message"] != tt.wantMessage {
+			t.Fatalf("expected message %q, got %q", tt.wantMessage, l["@message"])
+		}
+	}
+}