github.com/slspeek/camlistore_namedsearch@v0.0.0-20140519202248-ed6f70f7721a/pkg/index/sniff.go (about)

     1  /*
     2  Copyright 2011 Google Inc.
     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 index
    18  
    19  import (
    20  	"bytes"
    21  	"errors"
    22  
    23  	"camlistore.org/pkg/blob"
    24  	"camlistore.org/pkg/magic"
    25  	"camlistore.org/pkg/schema"
    26  )
    27  
    28  type BlobSniffer struct {
    29  	br blob.Ref
    30  
    31  	header    []byte
    32  	written   int64
    33  	meta      *schema.Blob // or nil
    34  	mimeType  string
    35  	camliType string
    36  }
    37  
    38  func NewBlobSniffer(ref blob.Ref) *BlobSniffer {
    39  	if !ref.Valid() {
    40  		panic("invalid ref")
    41  	}
    42  	return &BlobSniffer{br: ref}
    43  }
    44  
    45  func (sn *BlobSniffer) SchemaBlob() (meta *schema.Blob, ok bool) {
    46  	return sn.meta, sn.meta != nil
    47  }
    48  
    49  func (sn *BlobSniffer) Write(d []byte) (int, error) {
    50  	if !sn.br.Valid() {
    51  		panic("write on sniffer with invalid blobref")
    52  	}
    53  	sn.written += int64(len(d))
    54  	if len(sn.header) < schema.MaxSchemaBlobSize {
    55  		n := schema.MaxSchemaBlobSize - len(sn.header)
    56  		if len(d) < n {
    57  			n = len(d)
    58  		}
    59  		sn.header = append(sn.header, d[:n]...)
    60  	}
    61  	return len(d), nil
    62  }
    63  
    64  func (sn *BlobSniffer) Size() int64 {
    65  	return sn.written
    66  }
    67  
    68  func (sn *BlobSniffer) IsTruncated() bool {
    69  	return sn.written > schema.MaxSchemaBlobSize
    70  }
    71  
    72  func (sn *BlobSniffer) Body() ([]byte, error) {
    73  	if sn.IsTruncated() {
    74  		return nil, errors.New("index.Body: was truncated")
    75  	}
    76  	return sn.header, nil
    77  }
    78  
    79  // MIMEType returns the sniffed blob's content-type or the empty string if unknown.
    80  // If the blob is a Camlistore schema metadata blob, the MIME type will be of
    81  // the form "application/json; camliType=foo".
    82  func (sn *BlobSniffer) MIMEType() string { return sn.mimeType }
    83  
    84  func (sn *BlobSniffer) CamliType() string { return sn.camliType }
    85  
    86  func (sn *BlobSniffer) Parse() {
    87  	if sn.bufferIsCamliJSON() {
    88  		sn.camliType = sn.meta.Type()
    89  		sn.mimeType = "application/json; camliType=" + sn.camliType
    90  	} else {
    91  		sn.mimeType = magic.MIMEType(sn.header)
    92  	}
    93  }
    94  
    95  func (sn *BlobSniffer) bufferIsCamliJSON() bool {
    96  	buf := sn.header
    97  	if !schema.LikelySchemaBlob(buf) {
    98  		return false
    99  	}
   100  	blob, err := schema.BlobFromReader(sn.br, bytes.NewReader(buf))
   101  	if err != nil {
   102  		return false
   103  	}
   104  	sn.meta = blob
   105  	return true
   106  }