1	/*
     2	Copyright 2014 The Perkeep Authors
     3	
     4	Licensed under the Apache License, Version 2.0 (the "License");
     5	you may not use this file except in compliance with the License.
     6	You may obtain a copy of the License at
     7	
     8	     http://www.apache.org/licenses/LICENSE-2.0
     9	
    10	Unless required by applicable law or agreed to in writing, software
    11	distributed under the License is distributed on an "AS IS" BASIS,
    12	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13	See the License for the specific language governing permissions and
    14	limitations under the License.
    15	*/
    16	
    17	package blobserver
    18	
    19	import (
    20		"context"
    21		"errors"
    22		"regexp"
    23		"strconv"
    24		"strings"
    25	)
    26	
    27	// NewMultiBlobStreamer concatenates multiple BlobStreamers into one.
    28	func NewMultiBlobStreamer(streamers ...BlobStreamer) BlobStreamer {
    29		return multiStreamer{s: streamers}
    30	}
    31	
    32	type multiStreamer struct {
    33		s []BlobStreamer
    34	}
    35	
    36	var msTokenPrefixRx = regexp.MustCompile(`^(\d+):`)
    37	
    38	func (ms multiStreamer) StreamBlobs(ctx context.Context, dest chan<- BlobAndToken, contToken string) error {
    39		defer close(dest)
    40		part := 0
    41		if contToken != "" {
    42			pfx := msTokenPrefixRx.FindString(contToken)
    43			var err error
    44			part, err = strconv.Atoi(strings.TrimSuffix(pfx, ":"))
    45			if pfx == "" || err != nil || part >= len(ms.s) {
    46				return errors.New("invalid continuation token")
    47			}
    48			contToken = contToken[len(pfx):]
    49		}
    50		srcs := ms.s[part:]
    51		for len(srcs) > 0 {
    52			bs := srcs[0]
    53			subDest := make(chan BlobAndToken, 16)
    54			errc := make(chan error, 1)
    55			go func() {
    56				errc <- bs.StreamBlobs(ctx, subDest, contToken)
    57			}()
    58			partStr := strconv.Itoa(part)
    59			for bt := range subDest {
    60				select {
    61				case <-ctx.Done():
    62					return ctx.Err()
    63				case dest <- BlobAndToken{Blob: bt.Blob, Token: partStr + ":" + bt.Token}:
    64				}
    65			}
    66			if err := <-errc; err != nil {
    67				return err
    68			}
    69			// Advance to the next part:
    70			part++
    71			srcs = srcs[1:]
    72			contToken = ""
    73		}
    74		return nil
    75	}