Annotate some more errors

cache/disk/casblob/casblob.go

@@ -578,7 +578,7 @@ func WriteAndClose(zstd zstdimpl.ZstdImpl, r io.Reader, f *os.File, t Compressio
 
 		_, err = io.ReadFull(r, uncompressedChunk[0:chunkEnd])
 		if err != nil {
-			return -1, err
+			return -1, fmt.Errorf("Failed to read %d bytes: %w", chunkEnd+1, err)
 		}
 
 		compressedChunk := zstd.EncodeAll(uncompressedChunk[0:chunkEnd])
@@ -587,7 +587,7 @@ func WriteAndClose(zstd zstdimpl.ZstdImpl, r io.Reader, f *os.File, t Compressio
 
 		written, err := f.Write(compressedChunk)
 		if err != nil {
-			return -1, err
+			return -1, fmt.Errorf("Failed to write compressed chunk to disk: %w", err)
 		}
 
 		fileOffset += int64(written)
@@ -599,7 +599,7 @@ func WriteAndClose(zstd zstdimpl.ZstdImpl, r io.Reader, f *os.File, t Compressio
 	if err == nil {
 		return -1, fmt.Errorf("expected %d bytes but got at least %d more", size, bytesAfter)
 	} else if err != io.EOF {
-		return -1, err
+		return -1, fmt.Errorf("Failed to read chunk of size %d: %w", len(uncompressedChunk), err)
 	}
 
 	actualHash := hex.EncodeToString(hasher.Sum(nil))
@@ -611,18 +611,23 @@ func WriteAndClose(zstd zstdimpl.ZstdImpl, r io.Reader, f *os.File, t Compressio
 	// We know all the chunk offsets now, go back and fill those in.
 	_, err = f.Seek(chunkTableOffset, io.SeekStart)
 	if err != nil {
-		return -1, err
+		return -1, fmt.Errorf("Failed to seek to offset %d: %w", chunkTableOffset, err)
 	}
 
 	err = binary.Write(f, binary.LittleEndian, h.chunkOffsets)
 	if err != nil {
-		return -1, err
+		return -1, fmt.Errorf("Failed to write chunk offsets: %w", err)
 	}
 
 	err = f.Sync()
 	if err != nil {
-		return -1, err
+		return -1, fmt.Errorf("Failed to sync file: %w", err)
+	}
+
+	err = f.Close()
+	if err != nil {
+		return -1, fmt.Errorf("Failed to close file: %w", err)
 	}
 
-	return fileOffset, f.Close()
+	return fileOffset, nil
 }

cache/disk/disk.go

@@ -354,27 +354,27 @@ func (c *diskCache) writeAndCloseFile(r io.Reader, kind cache.EntryKind, hash st
 	if kind == cache.CAS && c.storageMode != casblob.Identity {
 		sizeOnDisk, err = casblob.WriteAndClose(c.zstd, r, f, c.storageMode, hash, size)
 		if err != nil {
-			return -1, err
+			return -1, fmt.Errorf("Failed to write compressed CAS blob to disk: %w", err)
 		}
 		closeFile = false
 		return sizeOnDisk, nil
 	}
 
 	if sizeOnDisk, err = io.Copy(f, r); err != nil {
-		return -1, err
+		return -1, fmt.Errorf("Failed to copy data to disk: %w", err)
 	}
 
 	if isSizeMismatch(sizeOnDisk, size) {
 		return -1, fmt.Errorf(
-			"sizes don't match. Expected %d, found %d", size, sizeOnDisk)
+			"Sizes don't match. Expected %d, found %d", size, sizeOnDisk)
 	}
 
 	if err = f.Sync(); err != nil {
-		return -1, err
+		return -1, fmt.Errorf("Failed to sync file to disk: %w", err)
 	}
 
 	if err = f.Close(); err != nil {
-		return -1, err
+		return -1, fmt.Errorf("Failed to close file: %w", err)
 	}
 	closeFile = false
 

utils/tempfile/tempfile.go

@@ -2,6 +2,7 @@ package tempfile
 
 import (
 	"errors"
+	"fmt"
 	"os"
 	"strconv"
 	"sync"
@@ -78,7 +79,8 @@ func (c *Creator) Create(base string, legacy bool) (*os.File, string, error) {
 		}
 
 		// Unexpected error.
-		return nil, "", err
+		return nil, "", fmt.Errorf("Unexpected error opening temp file: %w", err)
 	}
+
 	return nil, "", errNoTempfile
 }