Implement text/csv content encoding for the response writer

CHANGELOG.md

@@ -5,6 +5,7 @@
 - [#7120](https://github.com/influxdata/influxdb/issues/7120): Add additional statistics to query executor.
 - [#7135](https://github.com/influxdata/influxdb/pull/7135): Support enable HTTP service over unix domain socket. Thanks @oiooj
 - [#3634](https://github.com/influxdata/influxdb/issues/3634): Support mixed duration units.
+- [#7099](https://github.com/influxdata/influxdb/pull/7099): Implement text/csv content encoding for the response writer.
 
 ### Bugfixes
 

services/httpd/response_writer.go

@@ -1,9 +1,14 @@
 package httpd
 
 import (
+	"encoding/csv"
 	"encoding/json"
 	"io"
 	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/influxdata/influxdb/models"
 )
 
 // ResponseWriter is an interface for writing a response.
@@ -19,6 +24,8 @@ type ResponseWriter interface {
 func NewResponseWriter(w http.ResponseWriter, r *http.Request) ResponseWriter {
 	pretty := r.URL.Query().Get("pretty") == "true"
 	switch r.Header.Get("Accept") {
+	case "application/csv", "text/csv":
+		return &csvResponseWriter{statementID: -1, ResponseWriter: w}
 	case "application/json":
 		fallthrough
 	default:
@@ -62,3 +69,87 @@ func (w *jsonResponseWriter) Flush() {
 		w.Flush()
 	}
 }
+
+type csvResponseWriter struct {
+	statementID int
+	columns     []string
+	http.ResponseWriter
+}
+
+func (w *csvResponseWriter) WriteResponse(resp Response) (n int, err error) {
+	csv := csv.NewWriter(w)
+	for _, result := range resp.Results {
+		if result.StatementID != w.statementID {
+			// If there are no series in the result, skip past this result.
+			if len(result.Series) == 0 {
+				continue
+			}
+
+			// Set the statement id and print out a newline if this is not the first statement.
+			if w.statementID >= 0 {
+				// Flush the csv writer and write a newline.
+				csv.Flush()
+				if err := csv.Error(); err != nil {
+					return n, err
+				}
+
+				if out, err := io.WriteString(w, "\n"); err != nil {
+					return n, err
+				} else {
+					n += out
+				}
+			}
+			w.statementID = result.StatementID
+
+			// Print out the column headers from the first series.
+			w.columns = make([]string, 2+len(result.Series[0].Columns))
+			w.columns[0] = "name"
+			w.columns[1] = "tags"
+			copy(w.columns[2:], result.Series[0].Columns)
+			if err := csv.Write(w.columns); err != nil {
+				return n, err
+			}
+		}
+
+		for _, row := range result.Series {
+			w.columns[0] = row.Name
+			if len(row.Tags) > 0 {
+				w.columns[1] = string(models.Tags(row.Tags).HashKey()[1:])
+			} else {
+				w.columns[1] = ""
+			}
+			for _, values := range row.Values {
+				for i, value := range values {
+					switch v := value.(type) {
+					case float64:
+						w.columns[i+2] = strconv.FormatFloat(v, 'f', -1, 64)
+					case int64:
+						w.columns[i+2] = strconv.FormatInt(v, 10)
+					case string:
+						w.columns[i+2] = v
+					case bool:
+						if v {
+							w.columns[i+2] = "true"
+						} else {
+							w.columns[i+2] = "false"
+						}
+					case time.Time:
+						w.columns[i+2] = strconv.FormatInt(v.UnixNano(), 10)
+					}
+				}
+				csv.Write(w.columns)
+			}
+		}
+	}
+	csv.Flush()
+	if err := csv.Error(); err != nil {
+		return n, err
+	}
+	return n, nil
+}
+
+func (w *csvResponseWriter) Flush() {
+	if w, ok := w.ResponseWriter.(http.Flusher); ok {
+		w.Flush()
+	}
+}