[feature] Allow users to export data via the settings panel (#3140)

* [feature] Allow users to export data via the settings panel

* rename/move some stuff

internal/api/util/mime.go

@@ -35,6 +35,7 @@ const (
 	TextXML           = `text/xml`
 	TextHTML          = `text/html`
 	TextCSS           = `text/css`
+	TextCSV           = `text/csv`
 )
 
 // JSONContentType returns whether is application/json(;charset=utf-8)? content-type.

internal/api/util/negotiate.go

@@ -88,6 +88,12 @@ var HostMetaHeaders = []string{
 	AppXML,
 }
 
+// CSVHeaders just contains the text/csv
+// MIME type, used for import/export.
+var CSVHeaders = []string{
+	TextCSV,
+}
+
 // NegotiateAccept takes the *gin.Context from an incoming request, and a
 // slice of Offers, and performs content negotiation for the given request
 // with the given content-type offers. It will return a string representation

internal/api/util/response.go

@@ -18,6 +18,7 @@
 package util
 
 import (
+	"encoding/csv"
 	"encoding/json"
 	"encoding/xml"
 	"io"
@@ -213,6 +214,47 @@ func EncodeXMLResponse(
 	putBuf(buf)
 }
 
+// EncodeCSVResponse encodes 'records' as CSV HTTP response
+// to ResponseWriter with given status code, using CSV content-type.
+func EncodeCSVResponse(
+	rw http.ResponseWriter,
+	r *http.Request,
+	statusCode int,
+	records [][]string,
+) {
+	// Acquire buffer.
+	buf := getBuf()
+
+	// Wrap buffer in CSV writer.
+	csvWriter := csv.NewWriter(buf)
+
+	// Write all the records to the buffer.
+	if err := csvWriter.WriteAll(records); err == nil {
+		// Respond with the now-known
+		// size byte slice within buf.
+		WriteResponseBytes(rw, r,
+			statusCode,
+			TextCSV,
+			buf.B,
+		)
+	} else {
+		// This will always be an csv error, we
+		// can't really add any more useful context.
+		log.Error(r.Context(), err)
+
+		// Any error returned here is unrecoverable,
+		// set Internal Server Error JSON response.
+		WriteResponseBytes(rw, r,
+			http.StatusInternalServerError,
+			AppJSON,
+			StatusInternalServerErrorJSON,
+		)
+	}
+
+	// Release.
+	putBuf(buf)
+}
+
 // writeResponseUnknownLength handles reading data of unknown legnth
 // efficiently into memory, and passing on to WriteResponseBytes().
 func writeResponseUnknownLength(