Add ::truncate to File interface

Fixes esp8266#3846

Author: earlephilhower

cores/esp8266/FS.cpp

@@ -114,6 +114,13 @@ File::operator bool() const {
     return !!_p;
 }
 
+bool File::truncate(uint32_t size) {
+    if (!_p)
+        return false;
+
+    return _p->truncate(size);
+}
+
 const char* File::name() const {
     if (!_p)
         return nullptr;

cores/esp8266/FS.h

@@ -74,6 +74,7 @@ class File : public Stream
     operator bool() const;
     const char* name() const;
     const char* fullName() const; // Includes path
+    bool truncate(uint32_t size);
 
     bool isFile() const;
     bool isDirectory() const;

cores/esp8266/FSImpl.h

@@ -34,6 +34,7 @@ class FileImpl {
     virtual bool seek(uint32_t pos, SeekMode mode) = 0;
     virtual size_t position() const = 0;
     virtual size_t size() const = 0;
+    virtual bool truncate(uint32_t size) = 0;
     virtual void close() = 0;
     virtual const char* name() const = 0;
     virtual const char* fullName() const = 0;

cores/esp8266/spiffs_api.h

@@ -29,7 +29,10 @@
 #undef max
 #undef min
 #include "FSImpl.h"
-#include "spiffs/spiffs.h"
+extern "C" {
+    #include "spiffs/spiffs.h"
+    #include "spiffs/spiffs_nucleus.h"
+};
 #include "debug.h"
 #include "flash_utils.h"
 
@@ -406,6 +409,17 @@ class SPIFFSFileImpl : public FileImpl
         return _stat.size;
     }
 
+    bool truncate(uint32_t size) override
+    {
+        CHECKFD();
+        spiffs_fd *sfd;
+        if (spiffs_fd_get(_fs->getFs(), _fd, &sfd) == SPIFFS_OK) {
+            return SPIFFS_OK == spiffs_object_truncate(sfd, size, 0);
+        } else {
+          return false;
+        }
+    }
+
     bool isFile() const override
     {
         // No such thing as directories on SPIFFS

libraries/SDFS/src/SDFS.h

@@ -251,6 +251,14 @@ class SDFSFileImpl : public FileImpl
         return _opened ? _fd->fileSize() : 0;
     }
 
+    bool truncate(uint32_t size) override
+    {
+        if (!_opened) {
+            return false;
+        }
+        return _fd->truncate(size);
+    }
+
     void close() override
     {
         if (_opened) {

tests/host/fs/test_fs.cpp

@@ -219,6 +219,18 @@ TEST_CASE("#1819 Can list all files with openDir(\"\")", "[fs][bugreport]")
     REQUIRE(files.size() == 4);
 }
 
+TEST_CASE("truncate", "[fs][spiffs]")
+{
+    SPIFFS_MOCK_DECLARE(64, 8, 512, "");
+    REQUIRE(SPIFFS.begin());
+    createFile("/file1", "some text");
+    auto f = SPIFFS.open("/file1", "r");
+    f.truncate(4);
+    f.close();
+    String s = readFile("/file1");
+    REQUIRE( s == "some" );
+}
+
 TEST_CASE("SDFS", "[sdfs]")
 {
     SDFS_MOCK_DECLARE();
@@ -320,3 +332,4 @@ TEST_CASE("Listfiles.ino example", "[sd]")
     REQUIRE(readFileSD("dir1/file3") == "nihao");
     REQUIRE(readFileSD("/dir2/dir3/file4") == "bonjour");
 }
+