---
title: account_decompress
description: Decompresses a previously compressed account using account data and state proof
source_url:
  html: https://thru.org/docs/spec/vm/syscalls/account_decompress/
  md: https://thru.org/docs/spec/vm/syscalls/account_decompress.md
---

# account_decompress

## Overview

The `account_decompress` syscall restores a compressed account by providing the account’s data and a state proof verifying the data’s authenticity. This allows retrieval of previously compressed account state.

## Syscall Code

**Code:** `0x09` (`TN_SYSCALL_CODE_ACCOUNT_DECOMPRESS`)

## C SDK Function

```c
ulong tsys_account_decompress(ulong account_idx, void const* meta, void const* data,
                              void const* proof, ulong proof_sz);
```

## Arguments

**`account_idx` · *ulong* · **required****

Index of the account to decompress. Must be writable in the transaction and currently compressed or non-existent.

**`meta` · *void const** · **required***\*

Pointer to the account metadata.

**`data` · *void const** · **required***\*

Pointer to the account data payload.

**`proof` · *void const** · **required***\*

Pointer to the state proof data.

**`proof_sz` · *ulong* · **required****

Size of the state proof data in bytes.

## Return Value

Returns a syscall result code:

**`Success` · *ulong***

- `TN_VM_SYSCALL_SUCCESS` (0) - Account decompressed successfully

**`Error Codes` · *ulong***

- `TN_VM_ERR_SYSCALL_INVALID_ACCOUNT_INDEX` (-8) - Account index out of bounds
- `TN_VM_ERR_SYSCALL_ACCOUNT_NOT_WRITABLE` (-10) - Account not writable in transaction
- `TN_VM_ERR_SYSCALL_ACCOUNT_ALREADY_EXISTS` (-15) - Account is already active (not compressed)
- `TN_VM_ERR_SYSCALL_ACCOUNT_IN_COMPRESSION_TIMEOUT` (-34) - Account in compression cooldown period
- `TN_VM_ERR_SYSCALL_INVALID_ACCOUNT_DATA_SIZE` (-35) - Invalid account data size
- `TN_VM_ERR_SYSCALL_INVALID_ADDRESS` (-22) - Invalid virtual address for data or proof
- `TN_VM_ERR_SYSCALL_INVALID_PROOF_LEN` (-32) - Proof size mismatch
- `TN_VM_ERR_SYSCALL_INVALID_PROOF_SLOT` (-33) - Proof references invalid block slot
- `TN_VM_ERR_SYSCALL_INVALID_STATE_PROOF` (-23) - State proof verification failed
- `TN_VM_ERR_SYSCALL_INSUFFICIENT_PAGES` (-26) - Not enough pages for account data
- `TN_VM_ERR_SYSCALL_STATE_BYTES_ADDED_OVERFLOW` (-47) - State bytes counter overflow during activation

## Resource Consumption

### Compute Units

- **Base cost**: `TN_VM_SYSCALL_BASE_COST` (512 units)
- **Data cost**: Additional units equal to account data size in bytes
- **Proof cost**: Additional units equal to proof size in bytes
- **Total formula**: `base_cost + data_sz + proof_sz`

### Memory Pages

- **Page allocation**: Pages allocated for restored account data
- **Data pages**: Number of pages based on account data size (page-aligned)
- **Metadata pages**: Pages for account metadata structure
- **Proof verification**: Temporary memory usage for proof validation

### State Counter Impact

- **GASC (Global Activated State Counter)**: Incremented by `TSDK_ACCOUNT_META_FOOTPRINT` bytes, plus restored data bytes (up to original data size)
- **Purpose**: Tracks activated state for the account decompression in the global state counter
- **Overflow protection**: Returns `TN_VM_ERR_SYSCALL_STATE_BYTES_ADDED_OVERFLOW` if counter would overflow

## Side Effects

- **Account restoration**: Restores account metadata and data from provided input
- **Flag clearing**: Removes COMPRESSED flag from the account
- **Memory allocation**: Allocates pages for the account data

## Data Format

The account data must be structured as:

```c
struct account_data {
    tsdk_account_meta_t metadata;  // Public account metadata view
    uchar data[];               // Account data payload
};
```

## State Proof Verification

- **Proof type**: Must be `TN_STATE_PROOF_TYPE_EXISTING`
- **Hash verification**: Computed account hash must match the proof
- **Block validation**: Proof must reference a valid historical block
- **State root**: Account hash must verify against the block’s state root

## Compression Timeout

Accounts have a compression timeout period during which they cannot be decompressed. This prevents rapid compress/decompress cycles.

## Usage Notes

- Account must be writable in the transaction (signer approval)
- Account data size must match the metadata’s declared data size
- The provided data is validated by computing and verifying its hash
- Account becomes fully active after successful decompression
- Sufficient pages must be available for the account data

## Example

```c
#include <thru-sdk/c/tn_sdk_syscall.h>

// Decompress a previously compressed account
ulong account_idx = 3;

// Prepare account data (metadata + data)
struct {
    tsdk_account_meta_t meta;
    uchar data[1024];
} account_data;

// Load the account data from storage/network
load_compressed_account_data(&account_data);

// Prepare state proof
uchar proof_data[2048];
ulong proof_size = load_decompression_proof(account_idx, proof_data);

ulong result = tsys_account_decompress(account_idx, &account_data.meta, account_data.data,
                                       proof_data, proof_size);

if (result == TN_VM_SYSCALL_SUCCESS) {
    // Account decompressed successfully
    // Account is now active and accessible
    // COMPRESSED flag cleared
    // Data is available for program use
}
```