Add Command.DisplayCLI method signature

Following the approach described in ipfs#115, define a new method signature on `Command` that supports full processing of the `Response` object when text encoding is requested.

Add an encoding check and dispatch to DisplayCLI in local, http client, and http handler code paths.

Unblocks resolution of `encoding` option processing in multiple go-ipfs issues.

- ipfs/kubo#7050 json encoding for `ls`
- ipfs/kubo#1121 json encoding for `add`
- ipfs/kubo#5594 json encoding for `stats bw`

cli/parse.go

@@ -48,7 +48,7 @@ func Parse(ctx context.Context, input []string, stdin *os.File, root *cmds.Comma
 	// if no encoding was specified by user, default to plaintext encoding
 	// (if command doesn't support plaintext, use JSON instead)
 	if enc := req.Options[cmds.EncLong]; enc == "" {
-		if req.Command.Encoders != nil && req.Command.Encoders[cmds.Text] != nil {
+		if req.Command.HasText() {
 			req.SetOption(cmds.EncLong, cmds.Text)
 		} else {
 			req.SetOption(cmds.EncLong, cmds.JSON)

cli/run.go

@@ -123,7 +123,7 @@ func Run(ctx context.Context, root *cmds.Command,
 	encType := cmds.EncodingType(encTypeStr)
 
 	// use JSON if text was requested but the command doesn't have a text-encoder
-	if _, ok := cmd.Encoders[encType]; encType == cmds.Text && !ok {
+	if encType == cmds.Text && !cmd.HasText() {
 		req.Options[cmds.EncLong] = cmds.JSON
 	}
 

command.go

@@ -11,6 +11,7 @@ package cmds
 import (
 	"errors"
 	"fmt"
+	"io"
 	"strings"
 
 	files "github.com/ipfs/go-ipfs-files"
@@ -66,6 +67,11 @@ type Command struct {
 	// encoding.
 	Encoders EncoderMap
 
+	// DisplayCLI provides console output in cases requiring
+	// access to a full response object rather than individual
+	// result values. It is always run in the local process.
+	DisplayCLI func(res Response, stdout, stderr io.Writer) error
+
 	// Helptext is the command's help text.
 	Helptext HelpText
 
@@ -194,6 +200,11 @@ func (c *Command) Resolve(pth []string) ([]*Command, error) {
 	return cmds, nil
 }
 
+// HasText is true if the Command has direct support for text output
+func (c *Command) HasText() bool {
+	return c.DisplayCLI != nil || (c.Encoders != nil && c.Encoders[Text] != nil)
+}
+
 // Get resolves and returns the Command addressed by path
 func (c *Command) Get(path []string) (*Command, error) {
 	cmds, err := c.Resolve(path)

executor.go

@@ -2,6 +2,9 @@ package cmds
 
 import (
 	"context"
+	"io"
+	"io/ioutil"
+	"os"
 )
 
 type Executor interface {
@@ -32,6 +35,33 @@ type executor struct {
 	root *Command
 }
 
+// GetLocalEncoder provides special treatment for text encoding
+// when Command.DisplayCLI field is non-nil, by defining an
+// Encoder that delegates to a nested emitter that consumes a Response
+// and writes to the underlying io.Writer using DisplayCLI.
+func GetLocalEncoder(req *Request, w io.Writer, def EncodingType) (EncodingType, Encoder, error) {
+	encType, enc, err := GetEncoder(req, w, def)
+	if err != nil {
+		return encType, nil, err
+	}
+
+	if req.Command.DisplayCLI != nil && encType == Text {
+		emitter, response := NewChanResponsePair(req)
+		go req.Command.DisplayCLI(response, w, ioutil.Discard)
+		return encType, &emitterEncoder{emitter: emitter}, nil
+	}
+
+	return encType, enc, nil
+}
+
+type emitterEncoder struct {
+	emitter ResponseEmitter
+}
+
+func (enc *emitterEncoder) Encode(value interface{}) error {
+	return enc.emitter.Emit(value)
+}
+
 func (x *executor) Execute(req *Request, re ResponseEmitter, env Environment) error {
 	cmd := req.Command
 

http/client.go

@@ -7,6 +7,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"os"
 	"strings"
 
 	"github.com/ipfs/go-ipfs-cmds"
@@ -132,6 +133,11 @@ func (c *client) Execute(req *cmds.Request, re cmds.ResponseEmitter, env cmds.En
 		}
 	}
 
+	if cmd.DisplayCLI != nil &&
+		cmds.GetEncoding(req, cmds.Undefined) == cmds.Text {
+		return cmd.DisplayCLI(res, os.Stdout, os.Stderr)
+	}
+
 	return cmds.Copy(re, res)
 }
 

http/responseemitter.go

@@ -27,7 +27,7 @@ var (
 
 // NewResponseEmitter returns a new ResponseEmitter.
 func NewResponseEmitter(w http.ResponseWriter, method string, req *cmds.Request, opts ...ResponseEmitterOption) (ResponseEmitter, error) {
-	encType, enc, err := cmds.GetEncoder(req, w, cmds.JSON)
+	encType, enc, err := cmds.GetLocalEncoder(req, w, cmds.JSON)
 	if err != nil {
 		return nil, err
 	}