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When working with Unicode files, the presence of a byte-order mark (BOM) can impact file parsing. While not all Unicode files contain a BOM, it's essential to account for these when dealing with cross-platform data.
Regrettably, the Go standard library lacks a built-in method for handling BOMs. However, several approaches allow you to manually check and process files with BOMs.
Using a Buffered Reader
By using a buffered reader between your file stream and the calling program, you can inspect the first few bytes and optionally discard the BOM if found. The following snippet demonstrates this approach:
<code class="go">import ( "bufio" "os" "log" ) func main() { fd, err := os.Open("filename") if err != nil { log.Fatal(err) } defer fd.Close() br := bufio.NewReader(fd) r, _, err := br.ReadRune() if err != nil { log.Fatal(err) } if r != '\uFEFF' { br.UnreadRune() // Not a BOM -- put the rune back } // Now work with br as if you would with fd }</code>
Using io.Seeker
Alternatively, you can use the io.Seeker interface to seek within the file stream. If the first three bytes are not a BOM, seek back to the beginning.
<code class="go">import ( "os" "log" "io" ) func main() { fd, err := os.Open("filename") if err != nil { log.Fatal(err) } defer fd.Close() bom := [3]byte _, err = io.ReadFull(fd, bom[:]) if err != nil { log.Fatal(err) } if bom[0] != 0xef || bom[1] != 0xbb || bom[2] != 0xbf { _, err = fd.Seek(0, 0) // Not a BOM -- seek back to the beginning if err != nil { log.Fatal(err) } } // The next read operation on fd will read real data }</code>
Both methods assume the file is encoded in UTF-8. If encoding information is unknown or differs, more complex approaches may be necessary. Remember to handle BOMs appropriately when working with Unicode files to ensure accurate parsing and data integrity.
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