Validate page being fetched at possition 'p' self identifies as page 'p'.

It's the easiest verification whether the page is actually written, or its 'random' garbage in the block.

Signed-off-by: Piotr Tabor <ptab@google.com>

page.go

@@ -2,6 +2,7 @@ package bbolt
 
 import (
 	"fmt"
+	"log"
 	"os"
 	"sort"
 	"unsafe"
@@ -53,6 +54,12 @@ func (p *page) meta() *meta {
 	return (*meta)(unsafeAdd(unsafe.Pointer(p), unsafe.Sizeof(*p)))
 }
 
+func (p *page) fastCheck(id pgid) {
+	if p.id != id {
+		log.Panicf("Page expected to be: %v, but self identifies as %v", id, p.id)
+	}
+}
+
 // leafPageElement retrieves the leaf node by index
 func (p *page) leafPageElement(index uint16) *leafPageElement {
 	return (*leafPageElement)(unsafeIndex(unsafe.Pointer(p), unsafe.Sizeof(*p),

tx.go

@@ -609,12 +609,15 @@ func (tx *Tx) page(id pgid) *page {
 	// Check the dirty pages first.
 	if tx.pages != nil {
 		if p, ok := tx.pages[id]; ok {
+			p.fastCheck(id)
 			return p
 		}
 	}
 
 	// Otherwise return directly from the mmap.
-	return tx.db.page(id)
+	p := tx.db.page(id)
+	p.fastCheck(id)
+	return p
 }
 
 // forEachPage iterates over every page within a given page and executes a function.