In the previous blog, we introduced how to implement the cross-program invocation via function
invoke and function
invoke_signed. In this post, we will introduce another basic topic - Program Upgrade.
2. Deploy an Upgradable Program
By default, all the deployed programs are deployed with the BPFLoaderUpgradeable loader in Solana, which means they can be upgraded. Apart from this, Solana provides the option
--final to ensure that the deployed program is immutable. In this case, BPFLoader2 loader will be used to deploy the program. Once deployed, the program can not be upgraded.
The BPFLoaderUpgradeable loader program manages three types of accounts, program accounts, program data accounts, and buffer accounts. In the process of deployment, a buffer account is created at first. After that, the Solana CLI loads the bytecodes of the target program and writes them into the buffer account. Eventually, the bytecodes stored in the buffer account will be copied into the program data account.
Thus, buffer accounts are used by the Upgradeable BPF loader to temporarily store the bytecodes during the deployment process, program data accounts store the real data of a program, and program accounts work as proxy which point to the corresponding program data accounts.
In the following, let’s go through a few samples on how to upgrade your program. All the code used in this post can be find here.
2.1 Code Review (Rectangle_Area)
In this sample contract, we define a struct named
Rectangle, which contains three attributes,
area from line 13 to line 17. We also define an
area() function for
Rectangle. The function
area() is to calculate the area of the rectangle using
process_instruction(), we first use function
unpack_u32() to extract the
width and the
height of the rectangle from the instruction data (line 45 - line 46). In line 51, the account used to store the data of the rectangle is extracted. In line 59, function
try_from_slice_unchecked() deserializes the data of the account with the type of struct
Rectangle. Next, we assign the data to corresponding fields of the struct and calculate the value of area (line 61 - line 63). The last step is to serialize the data, and write it back to the data account.
The deployed program can be find in the following link.
2.2 Send Transaction
On the client side, we first send a transaction to create an account for storing data. We set the space size as 1,024 bytes to ensure it is enough.
We then send another transaction to calculate the area of the rectangle and store it into the data account.
The transaction can be found in the following link.
Now, we want to add a new function in the program, which is to calculate the perimeter of the rectangle.
After compile the updated project, we upgrade the deployed program on-chain with the following command.
solana program deploy /path/to/program.so --program-id <PROGRAM_ID>
The contract can be upgraded directly and you can view the related transaction below.
We further send a transaction to the program to verify that it is upgraded successfully. The result shows the function works well
The related transaction can be found below.
4 Upgrade Again
This time we want to store the calculated perimeter into the data account. In this case, we add one more attribute
perimeter into the struct
Rectangle (line 18).
Since the struct of the data account is different from the previous one, we need to first read the data from the data account. We deserialize the stored data using the original struct (i.e., OldRectangle). After that, we assign the related attributes to the new struct (i.e., CurrentRectangle) and init the new attribute (i.e., perimeter).
Finally, we calculate the value of perimeter and assign it back to the
update_account before serializing it into the
The transaction for upgrading can be found below.
After upgrading, we can check the data stored in the account with the command
solana account <DataAccount>. You can find the attributes are stored in the first 32 bytes. The whole upgrading process is finished.
In this article, we introduce how a program can be upgraded in Solana. We use different examples to illustrate the detail process. Stay tuned and more articles for Solana will be posted.