diff --git a/clients/go/camput/camput.go b/clients/go/camput/camput.go
index 4345f2143..9de341914 100644
--- a/clients/go/camput/camput.go
+++ b/clients/go/camput/camput.go
@@ -45,24 +45,36 @@ var flagName = flag.String("name", "", "Optional name attribute to set on perman
 var flagTag = flag.String("tag", "", "Optional tag attribute to set on permanode when using -permanode and -file. Single value or comma separated ones.")
 
 var flagVerbose = flag.Bool("verbose", false, "be verbose")
+
 var flagUseStatCache = flag.Bool("statcache", false, "Use the stat cache, assuming unchanged files already uploaded in the past are still there. Fast, but potentially dangerous.")
+var flagUseHaveCache = flag.Bool("havecache", false, "Use the 'have cache', a cache keeping track of what blobs the remote server should already have from previous uploads.")
 
 var flagSetAttr = flag.Bool("set-attr", false, "set (replace) an attribute")
 var flagAddAttr = flag.Bool("add-attr", false, "add an attribute, additional if one already exists")
 
 var wereErrors = false
 
+// UploadCache is the "stat cache" for regular files.  Given a current
+// working directory, possibly relative filename, and stat info,
+// returns what the ultimate put result (the top-level "file" schema
+// blob) for that regular file was.
 type UploadCache interface {
 	CachedPutResult(pwd, filename string, fi *os.FileInfo) (*client.PutResult, os.Error)
 	AddCachedPutResult(pwd, filename string, fi *os.FileInfo, pr *client.PutResult)
 }
 
+type HaveCache interface {
+	BlobExists(br *blobref.BlobRef) bool
+	NoteBlobExists(br *blobref.BlobRef)
+}
+
 type Uploader struct {
 	*client.Client
 	entityFetcher jsonsign.EntityFetcher
 
-	pwd   string
-	cache UploadCache
+	pwd       string
+	statCache UploadCache
+	haveCache HaveCache
 
 	filecapc chan bool
 }
@@ -123,19 +135,17 @@ func (up *Uploader) UploadFile(filename string) (respr *client.PutResult, outerr
 		return nil, err
 	}
 
-	if up.cache != nil {
-		cachedRes, err := up.cache.CachedPutResult(up.pwd, filename, fi)
+	if up.statCache != nil && fi.IsRegular() {
+		cachedRes, err := up.statCache.CachedPutResult(up.pwd, filename, fi)
 		if err == nil {
 			vprintf("Cache HIT on %q -> %v", filename, cachedRes)
 			return cachedRes, nil
 		}
-		if fi.IsRegular() {
-			defer func() {
-				if respr != nil && outerr == nil {
-					up.cache.AddCachedPutResult(up.pwd, filename, fi, respr)
-				}
-			}()
-		}
+		defer func() {
+			if respr != nil && outerr == nil {
+				up.statCache.AddCachedPutResult(up.pwd, filename, fi, respr)
+			}
+		}()
 	}
 
 	m := schema.NewCommonFileMap(filename, fi)
@@ -203,17 +213,6 @@ func (up *Uploader) UploadFile(filename string) (respr *client.PutResult, outerr
 	return mappr, err
 }
 
-func (up *Uploader) UploadMap(m map[string]interface{}) (*client.PutResult, os.Error) {
-	json, err := schema.MapToCamliJson(m)
-	if err != nil {
-		return nil, err
-	}
-	if *flagVerbose {
-		fmt.Printf("json: %s\n", json)
-	}
-	return up.Upload(client.NewUploadHandleFromString(json))
-}
-
 func (up *Uploader) SignMap(m map[string]interface{}) (string, os.Error) {
 	camliSigBlobref := up.Client.SignerPublicKeyBlobref()
 	if camliSigBlobref == nil {
@@ -234,12 +233,34 @@ func (up *Uploader) SignMap(m map[string]interface{}) (string, os.Error) {
 	return sr.Sign()
 }
 
+func (up *Uploader) UploadMap(m map[string]interface{}) (*client.PutResult, os.Error) {
+	json, err := schema.MapToCamliJson(m)
+	if err != nil {
+		return nil, err
+	}
+	vprintf("json: %s\n", json)
+	return up.uploadString(json)
+}
+
 func (up *Uploader) UploadAndSignMap(m map[string]interface{}) (*client.PutResult, os.Error) {
 	signed, err := up.SignMap(m)
 	if err != nil {
 		return nil, err
 	}
-	return up.Upload(client.NewUploadHandleFromString(signed))
+	return up.uploadString(signed)
+}
+
+func (up *Uploader) uploadString(s string) (*client.PutResult, os.Error) {
+	uh := client.NewUploadHandleFromString(s)
+	if c := up.haveCache; c != nil && c.BlobExists(uh.BlobRef) {
+		vprintf("HaveCache HIT for %s / %d", uh.BlobRef, uh.Size)
+		return &client.PutResult{BlobRef: uh.BlobRef, Size: uh.Size, Skipped: true}, nil
+	}
+	pr, err := up.Upload(uh)
+	if err == nil && up.haveCache != nil {
+		up.haveCache.NoteBlobExists(uh.BlobRef)
+	}
+	return pr, err
 }
 
 func (up *Uploader) UploadNewPermanode() (*client.PutResult, os.Error) {
@@ -324,9 +345,14 @@ func main() {
 	}
 
 	if *flagUseStatCache {
-		cache := NewFlatCache()
+		cache := NewFlatStatCache()
 		defer cache.Save()
-		up.cache = cache
+		up.statCache = cache
+	}
+	if *flagUseHaveCache {
+		cache := NewFlatHaveCache()
+		defer cache.Save()
+		up.haveCache = cache
 	}
 
 	switch {
diff --git a/clients/go/camput/flatcache.go b/clients/go/camput/flatcache.go
index cb58db360..904278e50 100644
--- a/clients/go/camput/flatcache.go
+++ b/clients/go/camput/flatcache.go
@@ -24,6 +24,7 @@ import (
 	"reflect"
 	"sync"
 
+	"camli/blobref"
 	"camli/client"
 	"camli/osutil"
 )
@@ -33,18 +34,18 @@ type fileInfoPutRes struct {
 	Pr client.PutResult
 }
 
-// FlatCache is an ugly hack, until leveldb-go is ready
+// FlatStatCache is an ugly hack, until leveldb-go is ready
 // (http://code.google.com/p/leveldb-go/)
-type FlatCache struct {
+type FlatStatCache struct {
 	mu       sync.Mutex
 	filename string
 	m        map[string]fileInfoPutRes
 	dirty    map[string]fileInfoPutRes
 }
 
-func NewFlatCache() *FlatCache {
-	filename := filepath.Join(osutil.CacheDir(), "camput.cache")
-	fc := &FlatCache{
+func NewFlatStatCache() *FlatStatCache {
+	filename := filepath.Join(osutil.CacheDir(), "camput.statcache")
+	fc := &FlatStatCache{
 		filename: filename,
 		m:        make(map[string]fileInfoPutRes),
 		dirty:    make(map[string]fileInfoPutRes),
@@ -68,7 +69,7 @@ func NewFlatCache() *FlatCache {
 	return fc
 }
 
-var _ UploadCache = (*FlatCache)(nil)
+var _ UploadCache = (*FlatStatCache)(nil)
 
 var ErrCacheMiss = os.NewError("not in cache")
 
@@ -78,7 +79,7 @@ func cacheKey(pwd, filename string) string {
 	return filepath.Clean(pwd) + "\x00" + filepath.Clean(filename)
 }
 
-func (c *FlatCache) CachedPutResult(pwd, filename string, fi *os.FileInfo) (*client.PutResult, os.Error) {
+func (c *FlatStatCache) CachedPutResult(pwd, filename string, fi *os.FileInfo) (*client.PutResult, os.Error) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
@@ -96,7 +97,7 @@ func (c *FlatCache) CachedPutResult(pwd, filename string, fi *os.FileInfo) (*cli
 	return &pr, nil
 }
 
-func (c *FlatCache) AddCachedPutResult(pwd, filename string, fi *os.FileInfo, pr *client.PutResult) {
+func (c *FlatStatCache) AddCachedPutResult(pwd, filename string, fi *os.FileInfo, pr *client.PutResult) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	key := cacheKey(pwd, filename)
@@ -108,17 +109,17 @@ func (c *FlatCache) AddCachedPutResult(pwd, filename string, fi *os.FileInfo, pr
 	c.m[key] = val
 }
 
-func (c *FlatCache) Save() {
+func (c *FlatStatCache) Save() {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	if len(c.dirty) == 0 {
-		vprintf("FlatCache: Save, but nothing dirty")
+		vprintf("FlatStatCache: Save, but nothing dirty")
 		return
 	}
 
 	f, err := os.OpenFile(c.filename, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0600)
 	if err != nil {
-		log.Fatalf("FlatCache OpenFile: %v", err)
+		log.Fatalf("FlatStatCache OpenFile: %v", err)
 	}
 	defer f.Close()
 	e := gob.NewEncoder(f)
@@ -132,5 +133,73 @@ func (c *FlatCache) Save() {
 		write(v)
 	}
 	c.dirty = make(map[string]fileInfoPutRes)
-	log.Printf("FlatCache: saved")
+	log.Printf("FlatStatCache: saved")
+}
+
+type FlatHaveCache struct {
+	mu       sync.Mutex
+	filename string
+	m        map[string]bool
+	dirty    map[string]bool
+}
+
+func NewFlatHaveCache() *FlatHaveCache {
+	filename := filepath.Join(osutil.CacheDir(), "camput.havecache")
+	c := &FlatHaveCache{
+		filename: filename,
+		m:        make(map[string]bool),
+		dirty:    make(map[string]bool),
+	}
+	if f, err := os.Open(filename); err == nil {
+		defer f.Close()
+		d := gob.NewDecoder(f)
+		for {
+			var key string
+			if d.Decode(&key) != nil {
+				break
+			}
+			c.m[key] = true
+		}
+	}
+	return c
+}
+
+func (c *FlatHaveCache) BlobExists(br *blobref.BlobRef) bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.m[br.String()]
+}
+
+func (c *FlatHaveCache) NoteBlobExists(br *blobref.BlobRef) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	k := br.String()
+	c.m[k] = true
+	c.dirty[k] = true
+}
+
+func (c *FlatHaveCache) Save() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if len(c.dirty) == 0 {
+		vprintf("FlatHaveCache: Save, but nothing dirty")
+		return
+	}
+
+	f, err := os.OpenFile(c.filename, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0600)
+	if err != nil {
+		log.Fatalf("FlatHaveCache OpenFile: %v", err)
+	}
+	defer f.Close()
+	e := gob.NewEncoder(f)
+	write := func(v interface{}) {
+		if err := e.Encode(v); err != nil {
+			panic("Encode: " + err.String())
+		}
+	}
+	for k, _ := range c.dirty {
+		write(k)
+	}
+	c.dirty = make(map[string]bool)
+	log.Printf("FlatHaveCache: saved")
 }